Online Etymology Dictionary

prate (v.): early 15c., from or related to Middle Dutch praten "to chatter" (c.1400), from a West Germanic imitative root (cf. East Frisian proten, Middle Low German praten, Middle High German braten, Swedish prata "to talk, chatter"). Related: Prated; prating. As a noun from 1570s.
pratfall (n.): 1939, from prat "buttock" + fall (n.). "Chiefly N. Amer. slang" [OED]. As a verb from 1940.
Pratt: the surname apparently is from Old English *prætt (adj.) "cunning, astute;" related to late Old English noun prætt "a trick" (see pretty). As a type of pottery, named for Staffordshire pottery manufacturer Felix Pratt (1780-1859).
prattle (v.): 1530s, frequentative of prate (q.v.). Related: Prattled; prattling. The noun is attested from 1550s.
pravity (n.): "depravity," 1540s, from Latin pravitas "crookedness, distortion, deformity; impropriety, perverseness," from pravus "wrong, bad," literally "crooked."
prawn (n.): early 15c., prayne, of unknown origin. "No similar name found in other langs." [OED].
praxis (n.): 1580s, from Medieval Latin praxis "practice, exercise, action" (mid-13c., opposite of theory), from Greek praxis "practice, action, doing," from stem of prassein, prattein "to do, to act" (see practical).
pray (v.): early 13c., "ask earnestly, beg," also (c.1300) "pray to a god or saint," from Old French preier "to pray" (c.900, Modern French prier), from Vulgar Latin *precare (also source of Italian pregare), from Latin precari "ask earnestly, beg, entreat," from *prex (plural preces, genitive precis) "prayer, request, entreaty," from PIE root *prek- "to ask, request, entreat" (cf. Sanskrit prasna-, Avestan frashna- "question;" Old Church Slavonic prositi, Lithuanian prasyti "to ask, beg;" Old High German frahen, German fragen, Old English fricgan "to ask" a question).

Parenthetical expression I pray you, "please, if you will," attested from 1510s, contracted to pray 16c. Related: Prayed; praying. Praying mantis attested from 1809. The "Gardener's Monthly" of July 1861 lists other names for it as camel cricket, soothsayer, and rear horse.
prayer (n.): c.1300, from Old French prier "prayer, petition, request" (12c., Modern French prière), from Medieval Latin precaria "petition, prayer," noun use of Latin adjective precaria, fem. of precarius "obtained by prayer, given as a favor," from precari "to ask, beg, pray" (see pray). Related: Prayers.

Prayer-book attested from 1590s; prayer-meeting from 1780. To not have a prayer "have no chance" is from 1941.
prayerful (adj.): 1620s, from prayer + -ful. Related: Prayerfully; prayerfulness.
pre-: word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (cf. Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian pre "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "beyond" (see per).

The Latin word was active in forming verbs. Also cf. prae-. Sometimes in Middle English muddled with words in pro- or per-.
pre-arrange (v.): also prearrange, 1792 (implied in pre-arranged), from pre- + arrange. Related: Pre-arranging.
pre-arrangement (n.): also prearrangement, 1775, from pre- + arrangement.
pre-atomic (adj.): "before the atomic age," 1914, in "World Set Free" -- H.G. Wells anticipating the word the future would use to look back at a time defined by events that hadn't yet happened in his day; from pre- + atomic.
pre-date (v.): also predate, 1859, "to antedate, to assign an earlier date to," from pre- + date (n.1) "point in time." As "to exist before," from 1857. Related: Pre-dated; pre-dating.
pre-dawn (adj.): 1940, from pre- + dawn (n.).
pre-eclampsia (n.): also preeclampsia, 1903, from pre- + eclampsia, from Greek eklampsis "a shining forth," from ek- "out" (see ex-) + lampein "to shine" (see lamp). Related: Pre-eclamptic (1896).
pre-elect (v.): 1560s, from pre- + elect (v.). Related: Pre-elected; pre-electing.
pre-election (n.): 1580s, from pre- + election.
pre-electric (adj.): 1894, from pre- + electric.
pre-eminence (n.): also pre-eminence, c.1200, from Late Latin praeeminentia "distinction, superiority," from Latin praeeminentem (nominative praeeminens), present participle of praeeminere "transcend, excel," literally "project forward, rise above," from prae "before" (see pre-) + eminere "stand out, project" (see eminent).
pre-eminent (adj.): also preeminent, mid-15c., from Medieval Latin preeminentem, from Latin praeeminentem (nominative praeeminens), present participle of praeeminare "to transcend, excel," literally "to project forward, rise above" (see pre-eminence). Related: Pre-eminently; preeminently.
pre-empt (v.): also preempt, 1830, "secure by pre-emtion," back-formation from pre-emption, originally American English. In the broascasting sense, it is attested from 1965, American English, a euphemism for "cancel." Related: pre-empted; preempted.
pre-emption (n.): also preemption, c.1600, literally "the right of purchasing before others," from pre- "before" + emption.
pre-emptive (adj.): also preemptive, 1806, "pertaining to preemption;" from pre-emption + -ive. Specifically of an attack on an enemy who is plotting his own attack, 1958, a term from the Cold War. Related: Pre-emptively; preemptively.
pre-emptory (adj.): also preemptory, 1822, "relating to pre-emption," from pre-emption + -ory.
pre-engage (v.): "bind in advance by promise," 1640s, from pre- + engage (v.). Related: Pre-engaged; pre-engaging.
pre-exist (v.): 1590s, from pre- + exist. Related: Pre-existed; pre-existing.
pre-existence (n.): 1650s, from pre- + existence.
pre-existing (adj.): also preexisting, 1590s, past participle adjective from pre-exist. The medical insurance pre-existing condition is attested from 1942.
pre-law (adj.): "of or pertaining to study in preparation for law school," 1961, American English, from pre- + law (school).
pre-med (n.): "undergraduate student in preparation for medical school," 1934, from premedical. From 1941 as "a major in preparation for medical training." As an adjective from 1936.
pre-op (n.): 1913 as short for pre-operative (preparation).
pre-order (v.): 1630s, from pre- + order (v.). Marked in OED 2nd ed. as "rare." Related: Pre-ordered; pre-ordering.
pre-owned (adj.): 1961, American English, from pre- + owned. A euphemism for used.
pre-position (v.): "to position beforehand," 1946, from pre- + position (v.). Related: Pre-positioned; pre-positioning.
Pre-Raphaelite (n., adj.): c.1848, in reference to the "brotherhood" (founded 1847) of Holman Hunt, Dante Gabriel Rossetti, John Everett Millais, and others (seven in all) who, encouraged by Ruskin, sought to revive the naturalistic spirit of art in the age before Raphael Sanzio (1483-1520).
pre-record (v.): 1937, from pre- + record (v.). Related: Pre-recorded; pre-recording.
pre-registration (n.): also preregistration, 1901, from pre- + registration.
pre-release (adj.): 1916, in reference to motion pictures, from pre- + release (n.).
pre-teen (adj.): also preteen, 1926, from pre- + teen. As a noun, "pre-teen person," from 1962. Sub-teen (1944) also was used.
preach (v.): at first in late Old English predician, a loan word from Church Latin; reborrowed 12c. as preachen, from Old French preechier "to preach, give a sermon" (11c., Modern French précher), from Late Latin praedicare "to proclaim publicly, announce" (in Medieval Latin "to preach"), from Latin prae "before" (see pre-) + dicare "to proclaim, to say" (see diction). Related: Preached; preaching. To preach to the converted is recorded from 1867 (form preach to the choir attested from 1979).
preacher (n.): c.1200, from Old French preecheor "preacher" (Modern French prêcheur), from Latin praedicatorem (nominative praedicator) "public praiser, eulogist," literally "proclaimer" (see preach). Slang short form preach (n.) is recorded by 1968, American English.
preachment (n.): late 14c., "a preaching;" earlier "an annoying or tedious speech" (c.1300); see preach (v.) + -ment. Related: Preachments.
preachy (adj.): 1819, from preach + -y (2). Related: Preachiness.
preamble (n.): late 14c., from Old French preambule (13c.) and directly from Medieval Latin preambulum, neuter adjective used as a noun, properly "preliminary," from Late Latin praeambulus "walking before," from Latin prae- "before" (see pre-) + ambulare "to walk" (see amble (v.)).
preamplifier (n.): 1929, from pre- + amplifier. Shortened form pre-amp is attested from 1957.
preassembly (n.): 1921, from pre- + assembly.
prebend (n.): early 15c., from Old French prebende, earlier provende (12c.) and directly from Medieval Latin prebenda "allowance," from Late Latin praebenda "allowance, pension" (see provender). Related: Prebendary.
Precambrian (adj.): also Pre-Cambrian, 1861, from pre- + Cambrian.