a Middle English merger of Old English line "cable, rope; series, row, row of letters; rule, direction," and Old French ligne "guideline, cord, string; lineage, descent" (12c.), both from Latin linea "linen thread, string, plumb-line," also "a mark, bound, limit, goal; line of descent," short for linea restis "linen cord," and similar phrases, from fem. of lineus (adj.) "of linen," from linum "linen" (see linen).
The earliest sense in Middle English was "cord used by builders for taking measurements;" extended late 14c. to "a thread-like mark" (from sense "cord used by builders for making things level," mid-14c.), also "track, course, direction." Meaning "limit, boundary" (of a county, etc.) is from 1590s. The mathematical sense of "length without breadth" is from 1550s. From 1530s as "a crease of the face or palm of the hand." From 1580s as "the equator."
Sense of "things or people arranged in a straight line" is from 1550s. Now considered American English, where British English uses queue (n.), but the sense appears earliest in English writers. Sense of "chronologically continuous series of persons" (a line of kings, etc.) is from late 14c.
Meaning "one's occupation, branch of business" is from 1630s, according to OED probably from misunderstood KJV translation of II Corinthians x.16, "And not to boast in another mans line of things made ready to our hand," where line translates Greek kanon which probably meant "boundary, limit;" the phrase "in another man's line" being parenthetical.
Commercial meaning "class of goods in stock" is from 1930, so called from being goods received by the merchant on a line in the specific sense "order given to an agent" for particular goods (1834). Insurance underwriting sense is from 1899. Line of credit is from 1958.
Meaning "series of public conveyances" (coaches, later ships) is from 1786; meaning "continuous part of a railroad" is from 1825. Meaning "telegraph wire between stations" is from 1847 (later "telephone wire"). Meaning "cord bearing hooks used in fishing" is from c. 1300. Meaning "policy or set of policies of a political faction" is 1892, American English, from notion of a procession of followers; this is the sense in the political party line, and, deteriorated, it is the slang line that means "glib and plausible talk meant to deceive."
In British army, the Line (1802) is the regular, numbered troops, as distinguished from guards, auxiliaries, militia, etc. In the Navy (1704) it refers to the battle line (the sense in ship of the line, which is attested from 1706).
Dutch lijn, Old High German lina, German Leine, Old Norse lina "a cord, rope," are likewise from Latin. Spanish and Italian have the word in the learned form linea. In continental measurements, a subdivision of an inch (one-tenth or one-twelfth in England), attested in English from 1660s but never common. Also see lines.
To get a line on "acquire information about" is from 1903. To lay it on the line is from 1929 as "to pay money;" by 1954 as "speak plainly." End of the line "as far as one can go" is from 1948. One's line of work, meaning "pursuit, interest" is from 1957, earlier line of country (1861). Line-drawing is from 1891. A line-storm (1850) is a type supposed to happen in the 10 days or two weeks around the times the sun crosses the equator.
1530s spelling alteration (see wh-) of Middle English hore, from Old English hore "prostitute, harlot," from Proto-Germanic *hōran-, fem. *hōrā- (source also of Old Frisian hor "fornication," Old Norse hora "adulteress," Danish hore, Swedish hora, Dutch hoer, Old High German huora "prostitute;" in Gothic only in the masc. hors "adulterer, fornicator," also as a verb, horinon "commit adultery"), probably etymologically "one who desires," from PIE root *ka- "to like, desire," which in other languages has produced words for "lover; friend."
Whore itself is perhaps a Germanic euphemism for a word that has not survived. The Old English vowel naturally would have yielded *hoor, which is the pronunciation in some dialects; it might have shifted by influence of Middle English homonym hore "physical filth, slime," also "moral corruption, sin," from Old English horh. The wh- form became current 16c. A general term of abuse for an unchaste or lewd woman (without regard to money) from at least c. 1200. Of male prostitutes from 1630s. Whore of Babylon is from Revelation xvii.1, 5, etc. In Middle English with occasional plural forms horen, heoranna.
The word, with its derivatives, is now avoided polite speech; its survival in literature, so as it survives, is due to the fact that it is a favorite word with Shakspere (who uses it, with its derivatives, 99 times) and is common in the authorized English version of the Bible ... though the American revisers recommended the substitution of harlot as less gross .... [Century Dictionary]
Some equivalent words in other languages also derive from sources not originally pejorative, such as Bohemian nevestka, diminutive of nevesta "bride;" Dutch deern, German dirne originally "girl, lass, wench;" also perhaps Old French pute, perhaps literally "girl," fem. of Vulgar Latin *puttus (but perhaps rather from Latin putidus "stinking;" see poontang). Welsh putain "whore" is from French, probably via Middle English. Among other languages, Greek porne "prostitute" is related to pernemi "sell," with an original notion probably of a female slave sold for prostitution; Latin meretrix is literally "one who earns wages" (source of Irish mertrech, Old English miltestre "whore, prostitute").
The vulgar Roman word was scortum, literally "skin, hide." Another term was lupa, literally "she-wolf" (preserved in Spanish loba, Italian lupa, French louve; see wolf (n.)). And of course there was prostituta, literally "placed in front," thus "publicly exposed," from the fem. past participle of prostituere (see prostitute (n.)). Another Old Norse term was skækja, which yielded Danish skøge, Swedish sköka; probably from Middle Low German schoke, which is perhaps from schode "foreskin of a horse's penis," perhaps with the sense of "skin" (compare Latin scortum) or perhaps via an intermediary sense of "vagina." Spanish ramera, Portuguese rameira are from fem. form of ramero "young bird of prey," literally "little branch," from ramo "branch." Breton gast is cognate with Welsh gast "bitch," of uncertain origin. Compare also strumpet, harlot.
Old Church Slavonic ljubodejica is from ljuby dejati "fornicate," a compound from ljuby "love" + dejati "put, perform." Russian bljad "whore" derives from Old Church Slavonic bladinica, from bladu "fornication." Polish nierządnica is literally "disorderly woman." Sanskrit vecya is a derivation of veca- "house, dwelling," especially "house of ill-repute, brothel." Another term, pumccali, means literally "one who runs after men." Avestan jahika is literally "woman," but only of evil creatures; another term is kunairi, from pejorative prefix ku- + nairi "woman."