Online Etymology Dictionary

pertain (v.): early 14c., from Old French partenir "to belong to" and directly from Latin pertinere "to reach, stretch; relate, have reference to; belong, be the right of; be applicable," from per- "through" (see per) + tenere "to hold" (see tenet). Related: Pertained; pertaining.
pertinacious (adj.): 1620s, from pertinacy (late 14c.; see pertinacity) + -ous. Related: Pertinaciously.
pertinacity (n.): c.1500, from Middle French pertinacité (early 15c.), from Old French pertinace "obstinate, stubborn," from Latin pertinacem (nominative pertinax) "very firm, tenacious, steadfast, persevering," from per- "very" (see per) + tenax (see tenacious). It drove out earlier pertinacy (late 14c.).
pertinence (n.): 1650s, from French pertenance or formed in English from pertinent + -ence.
pertinent (adj.): late 14c., from Anglo-French purtinaunt (late 13c.), Old French partenant (mid-13c.) and directly from Latin pertinentem (nominative pertinens) "pertaining," present participle of pertinere "to relate, concern" (see pertain). Related: Pertinently.
perturb (v.): late 14c., from Old French perturber "disturb, confuse" (14c.) and directly from Latin perturbare "to confuse, disorder, disturb," especially of states of the mind, from per- "through" (see per) + turbare "disturb, confuse," from turba "turmoil, crowd" (see turbid). Related: Perturbed; perturbing.
perturbate (adj.): 1560s, from Latin perturbatus "troubled, disturbed, agitated," past participle of perturbare (see perturb).
perturbation (n.): late 14c., from Old French perturbacion "disturbance, confusion" (14c.) and directly from Latin perturbationem (nominative perturbatio) "confusion, disorder, disturbance," noun of action from past participle stem of perturbare (see perturb).
perturbed (adj.): 1510s, past participle adjective from perturb (v.).
pertussis (n.): "whooping cough," 1670s (Sydenham), from Modern Latin pertussis, from per- "thoroughly" + tussis "cough," of unknown origin.
Peru: from Spanish Peru, said to be from Quechua pelu "river." Related: Peruvian.
peruke (n.): 1540s, "natural head of hair," from Middle French perruque (late 15c.), from Italian perrucca "head of hair, wig," of uncertain origin; supposed by some to be connected to Latin pilus "hair," "but the phonetic difficulties are considerable" [OED]. Meaning "artificial head of hair, periwig" is attested from 1560s.
perusal (n.): c.1600, from peruse + -al (2).
peruse (v.): late 15c., "use up, wear out, go through," from Middle English per- "completely" (see per) + use (v.). Meaning "read carefully" is first recorded 1530s, but this could be a separate formation. Meaning "read casually" is from 19c. Related: Perused; perusing.
perv (n,): also perve, 1944, slang shortening of (sexual) pervert (n.). As a slang verb, by 1941 as "to act erotically" (intransitive), by 1959 as "to eroticize" something (transitive).
pervade (v.): 1650s, from Latin pervadere "spread or go through," from per- "through" + vadere "to go" (see vamoose). Related: Pervaded; pervading.
pervasive (adj.): 1750, from Latin pervas-, past participle stem of pervadere (see pervade) + -ive.
perverse (adj.): mid-14c., "wicked," from Old French pervers "unnatural, degenerate; perverse, contrary" (12c.) and directly from Latin perversus "turned away, contrary, askew," figuratively, "turned away from what is right, wrong, malicious, spiteful," past participle of pervertere "to corrupt" (see pervert (v.)). The Latin word is glossed in Old English by forcerred, from past participle of forcyrran "to avoid," from cierran "to turn, return." Meaning "wrong, not in accord with what is accepted" is from 1560s; sense of "obstinate, stubborn" is from 1570s. It keeps the non-sexual senses of pervert (v.) and allows the psychological ones to go with perverted. Related: Perversely; perverseness.
perversion (n.): late 14c., "action of turning aside from truth, corruption, distortion" (originally of religious beliefs), from Latin perversionem (nominative perversio) "a turning about," noun of action from past participle stem of pervertere (see pervert (v.)). Psychological sense of "disorder of sexual behavior in which satisfaction is sought through channels other than those of normal heterosexual intercourse" is from 1892, originally including homosexuality.
Perversions are defined as unnatural acts, acts contrary to nature, bestial, abominable, and detestable. Such laws are interpretable only in accordance with the ancient tradition of the English common law which ... is committed to the doctrine that no sexual activity is justifiable unless its objective is procreation. [A.C. Kinsey, et.al., "Sexual Behavior in the Human Male," 1948]
perversity (n.): 1520s, from Middle French perversité "depravity, degeneracy" (12c.), from Latin perversitatem (nominative perversitas) "forwardness, untowardness," from perversus (see perverse).
pervert (v.): c.1300 (transitive), "to turn someone aside from a right religious belief to a false or erroneous one," from Old French pervertir "pervert, undo, destroy" (12c.) and directly from Latin pervertere "overthrow, overturn," figuratively "to corrupt, subvert, abuse," literally "turn the wrong way, turn about," from per- "away" (see per) + vertere "to turn" (see versus).

Related: Perverted; perverting. Replaced native froward, which embodies the same image. Old English had mishweorfed "perverted, inverted," an identical formation to the Latin word using native elements.
pervert (n.): 1660s, "one who has forsaken a doctrine or system regarded as true, apostate," from pervert (v.). Psychological sense of "one who has a perversion of the sexual instinct" is attested from 1897 (Havelock Ellis), originally especially of homosexuals.
perverted (adj.): 1660s, "turned from the right way," past participle adjective from pervert (v.). With implied sexual sense by 1897.
pervious (adj.): "penetrable, accessible, permeable," 1610s, from Latin pervius "that may be passed through" (see impervious).
pesky (adj.): 1775, originally in New England dialect, perhaps a dialectal formation from pest (cf. plaguy "confounded, annoying, disagreeable"). Partridge suggests an origin in Essex dialect.
peso (n.): "Spanish coin," 1550s, from Spanish peso, literally "a weight," from Latin pensum, properly past participle of pendere "to hang, to cause to hang" (see pendant).
pessary (n.): c.1400, from Late Latin pessarium, from Greek pessarion "medicated tampon of wool or lint," diminutive of pessos "pessary," earlier "oval stone used in games," perhaps of Semitic origin.
pessimism (n.): 1794 "worst condition possible," borrowed (by Coleridge) from French pessimisme, formed (on model of French optimisme) from Latin pessimus "worst," originally "bottom-most," from PIE *ped-samo-, superlative of root *pes- "foot" (see foot (n.)). As a name given to the doctrines of Schopenhauer, Hartmann, etc., that this is the worst possible world, or that everything tends toward evil, it is first recorded 1835, from German pessimismus (Schopenhauer, 1819). The attempt to make a verb of it as pessimize (1862) did not succeed.
pessimist (n.): 1820, "one who habitually expects the worst" (Knowles' dictionary, 1835, defines it as "A universal complainer"), from 19c. French pessimiste (see pessimism).
pessimistic (adj.): 1866, from pessimist + -ic.
pest (n.): 1550s (in imprecations, "a pest upon ____," etc.), "plague, pestilence," from Middle French peste (1530s), from Latin pestis "deadly contagious disease; a curse, bane," of uncertain origin. Meaning "noxious or troublesome person or thing" first recorded c.1600.
pester (v.): 1520s, "to clog, entangle, encumber," probably a shortening of Middle French empestrer "place in an embarrassing situation" (Modern French empêtrer, Walloon epasturer), from Vulgar Latin *impastoriare "to hobble" (an animal), from Latin im- "in" + Medieval Latin pastoria (chorda) "(rope) to hobble an animal," from Latin pastoria, fem. of pastorius "of a herdsman," from pastor "herdsman" (see pastor (n.)). Sense of "annoy, trouble" (1560s) is from influence of pest. Related: Pestered; pestering.
pesticide (n.): 1939, a hybrid coined from English pest + Latinate -cide.
pestiferous (adj.): mid-15c., "mischievous, pernicious," figurative use of Latin pestiferus "that brings plague or destruction," variant of pestifer "bringing plague, destructive, noxious," from pestis "plague" (see pest) + ferre "carry" (see infer). Related: Pestiferously; pestiferousness.
pestilence (n.): c.1300, from Old French pestilence "plague, epidemic" (12c.) and directly from Latin pestilentia "a plague, an unwholesome atmosphere," noun of condition from pestilentem (nominative pestilens) "infected, unwholesome, noxious," from pestis "deadly disease, plague" (see pest).
pestilent (adj.): late 14c., from Latin pestilentem (nominative pestilens), from pestilis "of the nature of a plague," from pestis "deadly contagious disease" (see pest (n.)). Related: Pestilently.
pestilential (adj.): late 14c., from Medieval Latin pestilentialis, from Latin pestilentia "plague" (see pestilence). Related: Pestilentially.
pestle (n.): mid-14c. (as a surname late 13c.), from Old French pestel, from Latin pistillum "pounder, pestle," related to pinsere "to pound," from PIE *pis-to-, suffixed form of root *peis- "to crush" (cf. Sanskrit pinasti "pounds, crushes," pistah "anything ground, meal," Greek ptissein "to winnow," Old Church Slavonic pišo, pichati "to push, thrust, strike," pišenica "wheat," Russian pseno "millet").
pesto (n.): olive oil-based pasta sauce, 1937, from Italian pesto, contracted form of pestato, past participle of pestare "to pound, to crush," in reference to the crushed herbs and garlic in it, from Latin root of pestle.
pet (n.1): "tamed animal," originally in Scottish and northern England dialect (and exclusively so until mid-18c.), of unknown origin. Sense of "indulged child" (c.1500) is recorded slightly earlier than that of "animal kept as a favorite" (1530s), but the latter may be the primary meaning. Probably associated with or influenced by petty. As a term of endearment by 1849. Teacher's pet is attested from 1890. Pet-shop from 1928.
pet (n.2): "peevishness, offense at feeling slighted," 1580s, in phrase take the pet "take offense." Perhaps from pet (n.1) on a similar notion to that in American English that gets my goat, but the underlying notion is obscure, and the form of the original expression makes this doubtful. This word seems to have been originally a southern English term, while pet (n.1) was northern and Scottish.
pet (v.): 1620s, "treat as a pet," from pet (n.1). Sense of "to stroke" is first found 1818. Slang sense of "kiss and caress" is from 1920 (implied in petting). Related: Petted.
pet peeve (n.): "thing that provokes one most," 1919, from pet (n.1) in the adjectival sense "especially cherished" (1826), here in jocular or ironic use with peeve (n.).
PETA: acronym for People for the Ethical Treatment of Animals; the group’s website says it was founded in 1980.
petal (n.): 1726 (earlier petala, 1704), from Modern Latin petalum "petal" (17c.), from Greek petalon "a leaf; leaf of metal, thin plate," noun use of neuter of adj. petalos "outspread, broad, flat," from PIE root *pete- "to spread out" (see pace (n.)). Related: Petaline.
petard (n.): 1590s, "small bomb used to blow in doors and breach walls," from French pétard (late 16c.), from Middle French péter "break wind," from Old French pet "a fart," from Latin peditum, noun use of neuter past participle of pedere "to break wind," from PIE root *pezd- "to fart" (see feisty). Surviving in phrase hoist with one's own petard (or some variant) "blown up with one's own bomb," which is ultimately from Shakespeare (1605):
For tis the sport to haue the enginer Hoist with his owne petar ("Hamlet" III.iv.207).
See hoist.
petcock (n.): also pet-cock, 1864, from cock (n.2); the signification of the first element is uncertain.
Pete: familiar form of masc. proper name Peter. For Pete's sake is attested from 1903 in a list of children's expressions published in Massachusetts, probably a euphemistic use of the disciple's name in place of Christ; as an exclamation or quasi-oath, Peter! was in use 14c., but this likely is not connected to the modern use.
petechia (n.): plural petechiae, "small crimson or purple spots on skin," c.1795 (from 1580s in English texts as an Italian word), Modern Latin, from Italian petecchia "specks or freckles on the face," in plural form petecchie "measles," of unknown origin. Related: Petechial.
Peter: masc. proper name, 12c., from Old English Petrus (genitive Pet(e)res, dative Pet(e)re), from Latin Petrus, from Greek Petros, literally "stone, rock," translation of Syriac kefa "stone" (Latinized as Cephas), nickname Jesus gave to apostle Simon Bar-Jona (Matt. xvi:17), historically known as St. Peter, and consequently a popular name among Christians (e.g. Italian Pietro, Spanish and Portuguese Pedro, Old French Pierres, French Pierre, etc.). Slang for "penis" is attested from 1902, probably from identity of first syllable.

The common form of this very common name in medieval England was Peres (Anglo-French Piers), hence surnames Pierce, Pearson, etc. Among the diminutive forms were Parkin and Perkin. To rob Peter to pay Paul (1510s, also in early 17c. French as descouvrir S. Pierre pour couvrir S. Pol) might be a reference to the many churches dedicated to those two saints, and have sprung from the fairly common practice of building or enriching one church with the ruins or revenues of another. But the alliterative pairing of the two names is attested from c.1400 with no obvious connection to the saints:
Sum medicyne is for peter þat is not good for poul, for þe diuersite of complexioun. [Lanfranc's "Chirurgia Magna," English translation]