Online Etymology Dictionary

Paddy (n.2): "Irishman," 1780, slang, from the pet form of the common Irish proper name Patrick (Irish Padraig). It was in use in African-American vernacular by 1946 for any "white person." Paddy wagon is 1930, perhaps so called because many police officers were Irish. Paddywhack (1881) originally meant "an Irishman."
padlock (n.): "removable lock," late 15c., from lokke (see lock (n.)), but the first element is of unknown origin.
padlock (v.): 1640s, from padlock (n.). Related: Padlocked; padlocking.
padre (n.): "priest, chaplain," 1580s, from Italian, Spanish, or Portuguese padre, from Latin patrem (nominative pater) "father" (see father (n.)). The title of the regular clergy in those languages. Papar was the name the Norse gave to Irish monks whom they found in Iceland when they arrived.
Padua: Italian city, Italian Padova, from Latin Patavium, probably from Gaulish *padi "pine," in reference to the pine forests thereabouts. Related: Paduan.
paean (n.): 1590s, from Latin paean "hymn of deliverance," from Greek paian "hymn, chant, hymn to Apollo," from Paian, a name of the god of healing; originally the physician of the gods (in Homer), later merged with Apollo; literally "one who touches" (i.e. "one who heals by a touch"), from paio "to touch, strike."
paederasty (n.): see pederasty.
paediatric (adj.): see pediatric.
paediatrician (n.): see pediatrician; also see pedo-.
paediatrics (n.): see pediatrics.
paedo-: see pedo-.
paedophile (n.): see pedophile; also see pedo-.
paedophilia (n.): see pedophilia; also see pedo-.
Paedophryne (n.): frog genus, 2010, literally "child toad," from Greek paedo- "child" (see pedo-) + phryne typically "toad," but occasionally "frog" (the usual Greek for "frog" was batrakhos), which is perhaps from PIE *bher- (3) "shining, brown," or else from a local pre-Greek word. It includes Paedophryne amauensis, which was formally named 2012 and is considered the world's smallest vertebrate. The amauensis is from Amau village in Papua New Guinea, near which it was first found.
paella (n.): 1892, from Catalan paella, from Old French paele "cooking or frying pan" (Modern French poêle), from Latin patella "pan, dish" (see pail). So called for the pan in which it is cooked.
paeon (n.): metrical foot of one long and three short syllables (in any order), c. 1600, from Latin paeon, from Greek paion (see paean). Related: Paeonic.
paesan (n.): 1930s, "fellow countryman, native of one's own country," from Italian dialect, from Late Latin pagensis "peasant, rustic" (see peasant). Spanish form paisano attested in English (New Mexico) from 1844.
pagan (n.): late 14c., from Late Latin paganus "pagan," in classical Latin "villager, rustic; civilian, non-combatant" noun use of adjective meaning "of the country, of a village," from pagus "country people; province, rural district," originally "district limited by markers," thus related to pangere "to fix, fasten," from PIE root *pag- "to fix" (see pact). As an adjective from early 15c.

Religious sense is often said to derive from conservative rural adherence to the old gods after the Christianization of Roman towns and cities; but the word in this sense predates that period in Church history, and it is more likely derived from the use of paganus in Roman military jargon for "civilian, incompetent soldier," which Christians (Tertullian, c.202; Augustine) picked up with the military imagery of the early Church (such as milites "soldier of Christ," etc.). Applied to modern pantheists and nature-worshippers from 1908.
Pagan and heathen are primarily the same in meaning; but pagan is sometimes distinctively applied to those nations that, although worshiping false gods, are more cultivated, as the Greeks and Romans, and heathen to uncivilized idolaters, as the tribes of Africa. A Mohammedan is not counted a pagan much less a heathen. [Century Dictionary, 1902]
The English surname Paine, Payne, etc., appears by old records to be from Latin paganus, but whether in the sense "villager," "rustic," or "heathen" is disputed. It also was a common Christian name in 13c., "and was, no doubt, given without any thought of its meaning" ["Dictionary of English Surnames"].
paganism (n.): early 15c., from Church Latin paganismus, from paganus (see pagan).
page (n.1): "sheet of paper," 1580s, from Middle French page, from Old French pagene "page, text" (12c.), from Latin pagina "page, leaf of paper, strip of papyrus fastened to others," related to pagella "small page," from pangere "to fasten," from PIE root *pag- "to fix" (see pact).

Earlier pagne (12c.), directly from Old French. Usually said to be from the notion of individual sheets of paper "fastened" into a book. Ayto and Watkins offer an alternative theory: vines fastened by stakes and formed into a trellis, which led to sense of "columns of writing on a scroll." When books replaced scrolls, the word continued to be used. Related: Paginal. Page-turner "book that one can't put down" is from 1974.
page (n.2): "youth, lad, boy of the lower orders," c. 1300, originally also "youth preparing to be a knight," from Old French page "a youth, page, servant" (13c.), possibly via Italian paggio (Barnhart), from Medieval Latin pagius "servant," perhaps ultimately from Greek paidion "boy, lad," diminutive of pais (genitive paidos) "child."

But OED considers this unlikely and points instead to Littré's suggestion of a source in Latin pagus "countryside," in sense of "boy from the rural regions" (see pagan). Meaning "youth employed as a personal attendant to a person of rank" is first recorded mid-15c.; this was transferred from late 18c. to boys who did personal errands in hotels, clubs, etc., also in U.S. legislatures.
page (v.1): "to summon or call by name," 1904, from page (n.2), on the notion of "to send a page after" someone. Related: Paged; paging.
page (v.2): "to turn pages," 1620s, from page (n.1). Related: Paged; paging.
pageant (n.): late 14c., "play in a cycle of mystery plays," from Medieval Latin pagina, of uncertain origin, perhaps from Latin pagina "page of a book" (see page (n.1)) on notion of "manuscript" of a play.

But an early sense in Middle English also was "stage or scene of a play" (late 14c.) and Klein says a sense of Latin pagina was "movable scaffold" (probably from the etymological sense of "stake"). With excrescent -t as in ancient (adj.). Generalized sense of "showy parade, spectacle" is first attested 1805, though this notion is found in pageantry (1650s).
pageantry (n.): "splendid display," 1650s; see pageant + -ry.
pager (n.): "device that emits a signal when activated by a telephone call," 1968, agent noun from page (v.1).
paginate (v.): "to mark or number the pages of a publication," 1858 (implied in paginated), back-formation from pagination. Medieval Latin had paginare, but it had another sense. Related: Paginating.
pagination (n.): "action of marking page numbers," 1841, probably from French pagination (1835), from Latin pagina (see page (n.1)).
pagoda (n.): 1580s, pagode (modern form from 1630s), from Portuguese pagode (early 16c.), perhaps from a corruption of Persian butkada, from but "idol" + kada "dwelling." Or perhaps from or influenced by Tamil pagavadi "house belonging to a deity," from Sanskrit bhagavati "goddess," fem. of bhagavat "blessed, adorable," from *bhagah "good fortune," from PIE root *bhag- "to share out, apportion" (source also of Greek phagein "to eat;" see -phagous).
Pahlavi (n.): 1773, Iranian language spoken in Persia 3c.-10c., from Persian Pahlavi, from Old Persian Parthava "Parthia" (see Parthian).
pahoehoe (n.): "ropy lava," 1859, from Hawaiian.
Paige: fem. proper name, also a family name, variant of page (n.2) "young servant."
pail (n.): mid-14c., of uncertain origin, probably from Old French paele, paelle "cooking or frying pan, warming pan;" also a liquid measure, from Latin patella "small pan, little dish, platter," diminutive of patina "broad shallow pan, stewpan" (see pan (n.)).

Old English had pægel "wine vessel," but etymology does not support a connection. This Old English word possibly is from Medieval Latin pagella "a measure," from Latin pagella "column," diminutive of pagina (see page (n.1)).
paillard (n.): variant of palliard.
pain (n.): late 13c., "punishment," especially for a crime; also "condition one feels when hurt, opposite of pleasure," from Old French peine "difficulty, woe, suffering, punishment, Hell's torments" (11c.), from Latin poena "punishment, penalty, retribution, indemnification" (in Late Latin also "torment, hardship, suffering"), from Greek poine "retribution, penalty, quit-money for spilled blood," from PIE *kwei- "to pay, atone, compensate" (see penal). The earliest sense in English survives in phrase on pain of death.

Phrase to give (someone) a pain "be annoying and irritating" is from 1908; localized as pain in the neck (1924) and pain in the ass (1934), though this last might have gone long unrecorded and be the original sense and the others euphemisms. Pains "great care taken (for some purpose)" is first recorded 1520s (in the singular in this sense, it is attested from c. 1300). First record of pain-killer is from 1853.
pain (v.): c. 1300, "to exert or strain oneself, strive; endeavor," from Old French pener (v.) "to hurt, cause pain," from peine, and from Middle English peine (n.); see pain (n.). Transitive meaning "cause pain; inflict pain" is from late 14c. That of "to cause sorrow, grief, or unhappiness" also is from late 14c. Related: Pained; paining.
painful (adj.): mid-14c., from pain (n.) + -ful. Related: Painfully; painfulness.
painless (adj.): 1560s, from pain (n.) + -less. Related: Painlessly; painlessness.
painstaking: 1550s (n.), 1690s (adj.), paynes taking, from plural of pain (n.) + present participle of take (v.). Related: Painstakingly.
paint (v.): early 13c., "represent in painting or drawing, portray;" early 14c., "paint the surface of, color, stain;" from Old French peintier "to paint," from peint, past participle of peindre "to paint," from Latin pingere "to paint, represent in a picture, stain; embroider, tattoo," from PIE root *peig- (1), also *peik- "to cut" (source also of Sanskrit pimsati "hews out, cuts, carves, adorns," Old Church Slavonic pila "file, saw," Lithuanian pela "file").

Sense evolution between PIE and Latin was, presumably, from "decorate with cut marks" to "decorate" to "decorate with color." Compare Sanskrit pingah "reddish," pesalah "adorned, decorated, lovely," Old Church Slavonic pegu "variegated;" Greek poikilos "variegated;" Old High German fehjan "to adorn;" Old Church Slavonic pisati, Lithuanian piesiu "to write." Probably also representing the "cutting" branch of the family is Old English feol (see file (n.2)).

To paint the town (red) "go on a spree" first recorded 1884; to paint (someone or something) black "represent it as wicked or evil" is from 1590s. Adjective paint-by-numbers "simple" is attested by 1970; the art-for-beginners kits themselves date to c. 1953.
paint (n.): late 13c. (in compounds), "that with which something is painted," from paint (v.). Of rouge, make-up, etc., from 1650s. Paint brush attested from 1827.
painted (adj.): c. 1300, "depicted in a picture;" early 15c., "coated with paint," past participle adjective from paint (v.).
painter (n.1): "artist who paints pictures," early 14c., from Old French peintor, from Latin pictor "a painter," from pingere (see paint (v.)). Sense of "workman who colors surfaces with paint" is from c. 1400. As a surname, Painter is attested from mid-13c. but it is difficult to say which sense is meant. Related: Painterly.
painter (n.2): mid-14c., "rope or chain that holds an anchor to a ship's side," from Old French peintor, ultimately from Latin pendere "to weigh" (see pendant).
painting (n.): c. 1200, "that which is painted, a painting," verbal noun from paint (v.). From mid-15c. as "art of depicting by means of paint."
pair (n.): mid-13c., "two of a kind coupled in use," from Old French paire "pair, couple," and directly from Medieval Latin paria "equals," neuter plural of Latin par (genitive paris) "a pair, counterpart, equal," noun use of par (adj.) "equal, equal-sized, well-matched" (see par (n.)). Originally of things. Of persons from late 14c. Meaning "a woman's breasts" is attested from 1922. Pair bond (v.) is first attested 1940, in reference to birds mating.
pair (v.): "to come together with another; be mated or married" (intransitive), also "to make a pair by matching" (transitive), c. 1600, from pair (n.). These senses now often are distinguished by pair off (c. 1803) for the former and pair up (1908) for the latter. Related: Paired; pairing.
paisano: see paesan.
paisley (n.): 1834 as a type of clothing or material, from Paisley, town in southwest Scotland, where the cloth was originally made. As an adjective by 1900. The town name is literally "church," from Middle Irish baslec, itself from Latin basilica (see basilica).
pajama: see pajamas.