Online Etymology Dictionary

pat (adv.): "aptly, suitably, at the right time," 1570s, perhaps from pat (adj.) in sense of "that which hits the mark," a special use from pat (n.) in sense of "a hitting" of the mark. The modern adjective is 1630s, from the adverb.
pat (v.): 1560s, "to hit, throw;" meaning "to tap or strike lightly" is from 1714; from pat (n.). Related: Patted; patting. The nursery rhyme phrase pat-a-cake is known from 1823. Alternative patty-cake (usually American English) is attested from 1794 (in "Mother Goose's Melody, or Sonnets for the Cradle," Worcester, Mass.).
Pat: as a fem. proper name, short for Patricia. As a masc. proper name, short for Patrick; hence a nickname for any Irishman.
Patagonia: South American region, with -ia + Patagon, name given by Europeans to the Tehuelche people who inhabited the coasts of the region, sometimes said to mean literally "large-foot," from Spanish and Portuguese pata "paw, animal foot" (see patten) in reference to the people's llama-skin shoes. But elsewhere said to be from Patagon, name of a dog-headed monster in the prose romance "Amadís de Gaula" (1508) by Garci Ordóñez de Montalvo (which also might have yielded California).
patch (v.): mid-15c., from patch (n.1). Electronics sense of "to connect temporarily" is attested from 1923. Related: Patched; patching.
patch (n.1): "piece of cloth used to mend another material," late 14c., of obscure origin, perhaps a variant of pece, pieche, from Old North French pieche (see piece (n.)), or from an unrecorded Old English word. Phrase not a patch on "nowhere near as good as" is from 1860.
patch (n.2): "fool, clown," 1540s, perhaps from Italian pazzo "fool," of unknown origin. Possibly from Old High German barzjan "to rave" [Klein]. But Buck says pazzo is originally euphemistic, and from Latin patiens "suffering," in medical use, "the patient." Form perhaps influenced by folk etymology derivation from patch (n.1), on notion of a fool's patched garb.
patchouli (n.): perfume made from an Indian plant of the mint family, 1845, from the native name for the plant in Madras, said to be from Tamil pachchai "green" + ilai "leaf." The form of the word appears French, but this has not been explained and the record of it in English predates that in French.
patchwork (n.): "work composed of patches," 1690s, from patch (n.1) + work (n.). As an adjective from 1713.
patchy (adj.): 1798, from patch (n.1) + -y (2).
pate (n.1): "top of the head," early 14c. (late 12c. in surnames), of unknown origin; perhaps a shortened form of Old French patene or Medieval Latin patena, both from Latin patina "pan, dish" (see pan (n.)).
pate (n.2): "paste," 1706, from French pâté, from Old French paste, earlier pastée, from paste (see paste (n.)).
patella (n.): "knee cap," 1690s, from Latin patella "pan, kneecap," diminutive of patina "pan" (see pan (n.)). So called from its shape. Related: Patellar; patelliform.
paten (n.): "plate for bread at Eucharist," c.1300, from Old French patene and directly, from Medieval Latin patena, from Latin patina "pan, dish" (see pan (n.)).
patency (n.): 1650s, from patent + -cy.
patent (n.): late 14c., "open letter or document from some authority," shortened form of Anglo-French lettre patent (also in Medieval Latin (litteræ) patentes), literally "open letter" (late 13c.), from Old French patente (see patent (adj.).
The Letters Patent were ... written upon open sheets of parchment, with the Great Seal pendent at the bottom ... [while] the 'Litteræ Clausæ,' or Letters Close, ... being of a more private nature, and addressed to one or two individuals only, were closed or folded up and sealed on the outside. [S.R. Scargill-Bird, "A Guide to the Principal Classes of Documents at the Public Record Office," 1891]
Meaning "a license covering an invention" is from 1580s.
patent (v.): "to obtain right to land," 1670s, from patent (n.). The meaning "copyright an invention" is first recorded 1822, from earlier meaning "obtain exclusive right or monopoly" (1789), a privilege granted by the Crown via letters patent. Related: Patented; patenting.
patent (adj.): late 14c., in letters patent, literally "open letter," from Old French patente, from Latin patentum (nominative patens) "open, lying open," present participle of patere "lie open, be open," from PIE *pete- "to spread" (see pace (n.)). Sense of "open to view, plain, clear" is first recorded c.1500. Related: Patently.
paterfamilias (n.): early 15c., from Latin pater familias "master of a house, head of a family," from pater "father" (see father (n.)) + familias, old genitive of familia "family" (see family).
paternal (adj.): early 15c., from Old French paternal "of a father" (12c.), from Medieval Latin paternalis, from Latin paternus "of a father, fatherly," from pater (see father (n.)).
paternalism (n.): "feeling of a father for his children," 1851; "government as by a father over his children," 1866, from paternal + -ism. Related: Paternalistic (1890).
paternity (n.): mid-15c., "condition of being a father," from Old French paternité (12c.), from Late Latin paternitatem (nominative paternitas) "fatherly care, fatherhood," from Latin paternus "of a father," from pater (see father (n.)). Originally in the ecclesiastical sense; literal sense first recorded 1580s. Meaning "paternal origin" is from 1868.
paternoster (n.): "the Lord's Prayer," Old English Pater Noster, from Latin pater noster "our father," first words of the Lord's Prayer in Latin. Meaning "set of rosary beads" first recorded mid-13c. Paternoster Row, near St. Paul's in London (similarly named streets are found in other cathedral cities), reflects the once-important industry of rosary bead-making.
path (n.): Old English paþ, pæþ "path, track," from West Germanic *patha- (cf. Old Frisian path, Middle Dutch pat, Dutch pad, Old High German pfad, German Pfad "path"), of unknown origin. The original initial -p- in a Germanic word is an etymological puzzle. Watkins says the word is "probably borrowed (? via Scythian) from Iranian *path-," from PIE root *pent- "to tread, go, pass" (cf. Avestan patha "way;" see find (v.)), but this is too much of a stretch for OED and others. In Scotland and Northern England, commonly a steep ascent of a hill or in a road.
Pathet Lao: communist guerrilla movement and political party in Laos, 1954, from Laotian Thai, literally "Land of the Lao."
pathetic (adj.): 1590s, "affecting the emotions, exciting the passions," from Middle French pathétique "moving, stirring, affecting" (16c.), from Late Latin patheticus, from Greek pathetikos "subject to feeling, sensitive, capable of emotion," from pathetos "liable to suffer," verbal adjective of pathein "to suffer" (see pathos). Meaning "arousing pity, pitiful" is first recorded 1737. Colloquial sense of "so miserable as to be ridiculous" is attested from 1937. Related: Pathetical (1570s); pathetically. Pathetic fallacy (1856, first used by Ruskin) is the attribution of human qualities to inanimate objects.
pathfinder (n.): 1839 (Cooper), from path + finder.
pathless (adj.): 1590s, from path + -less.
patho-: before vowels path-, word-forming element meaning "Suffering, disease," from Greek patho-, comb. form of pathos "suffering, disease" (see pathos).
pathogen (n.): 1880, a back-formation from pathogenic.
pathogenesis (n.): 1876, from patho- + genesis.
pathogenic (adj.): "producing disease," 1836, from French pathogénique, from Greek pathos "disease" (see pathos) + French -génique "producing" (see -gen). Related: Pathogenetic (1838); pathogenicity.
pathognomonic (adj.): 1640s (implied in pathognomonical), from patho- "disease, suffering" + Greek gnomonikos "able to judge," from gnomon "one who knows" (see gnomon).
pathologic (adj.): "pertaining to pathology," 1650s, from Greek pathologikos (see pathology).
pathological (adj.): 1680s, "pertaining to disease," formed in English from pathologic + -al (1). Sense of "worthy to be a subject of pathology, morbid, excessive" (e.g. pathological liar) is attested from 1845. Related: Pathologically.
pathologist (n.): 1640s, from pathology + -ist.
pathology (n.): "science of diseases," 1610s, from French pathologie (16c.), from medical Latin pathologia "study of disease," from Greek pathos "suffering" (see pathos) + -logia "study" (see -logy). In reference to the study of abnormal mental conditions from 1842. Ancient Greek pathologia was "study of the passions;" the Greek word for "science of diseases" was pathologike ("pathologics").
pathophysiology (adj.): 1952, from patho- + physiology.
pathos (n.): "quality that arouses pity or sorrow," 1660s, from Greek pathos "suffering, feeling, emotion, calamity," literally "what befalls one," related to paskhein "to suffer," and penthos "grief, sorrow;" from PIE root *kwent(h)- "to suffer, endure" (cf. Old Irish cessaim "I suffer," Lithuanian kenčiu "to suffer," pakanta "patience").
pathway (n.): 1530s, from path + way (n.). An etymological tautology.
patience (n.): c.1200, "quality of being patient in suffering," from Old French pacience "patience; sufferance, permission" (12c.) and directly from Latin patientia "patience, endurance, submission; quality of suffering," from patientem (nominative patiens), present participle of pati "to suffer, endure," from PIE root *pe(i)- "to damage, injure, hurt" (see passion).
Patience, n. A minor form of despair, disguised as a virtue. [Ambrose Bierce, "Devil's Dictionary," 1911]
Meaning "constancy in effort" is attested from 1510s. Meaning "card game for one person" is from 1816.
patient (adj.): mid-14c., "enduring without complaint," from Old French pacient and directly from Latin patientem (see patience). Related: Patiently.
patient (n.): "suffering or sick person under medical treatment," late 14c., from Old French pacient (n.), from the adjective, from Latin patientem (see patience).
patina (n.): "greenish film on old bronze," 1748, from French patine (18c.), from Italian patina, perhaps from Latin patina "dish, pan" (see pan (n.)), on the notion of encrustation on ancient bronze dishes. Sense of "refinement, cultural sophistication" first recorded 1933.
patio (n.): 1818, "inner court open to the sky," from Spanish patio probably from Old Provençal patu, pati "untilled land, communal pasture," from Latin pactum "agreement" (see pact). Another theory traces the Spanish word to Latin patere "to lie open." Meaning "paved and enclosed terrace beside a building" first recorded 1941. Patio furniture is attested from 1969.
patisserie (n.): 1784, from French pâtisserie "pastry shop," from pâtisser "pastry-seller, pastry-cook," from Old French pasticier (14c.), from Medieval Latin pasticium "pasty, composed of paste," from Late Latin pasta "paste, pastry cake" (see pasta).
patois (n.): "a provincial dialect," 1640s, from French patois "native or local speech" (13c.), of uncertain origin, probably from Old French patoier "handle clumsily, to paw," from pate "a paw," from Vulgar Latin *patta (see patten), from notion of clumsy manner of speaking. Cf. French pataud "properly, a young dog with big paws, then an awkwardly built fellow" [Brachet]. Especially in reference to Jamaican English from 1934.
patootie (n.): "sweetheart, pretty girl," colloquial American English, 1921, perhaps a corruption of potato (c.f. sweet potato). Sweet patootie is recorded from 1919 as a generic exclamation.
patri-: word-forming element used to make terms describing kinship of the father or the paternal line, from Latin patri-, comb. form of pater (see father (n.)).
patriarch (n.): late 12c., from Old French patriarche "one of the Old Testament fathers" (11c.) and directly from Late Latin patriarcha (Tertullian), from Greek patriarkhes "chief or head of a family," from patria "family, clan," from pater "father" (see father (n.)) + arkhein "to rule" (see archon). Also used as an honorific title of certain bishops in the early Church, notably those of Antioch, Alexandria, and Rome.