gayyoudaoicibaDictYouDict
gay: [13] English borrowed gay from Old French gai, an adjective of uncertain origin connected by some with Old High German gāhi ‘sudden, impulsive’. ‘Happy’ is its ancestral meaning, stretching back to Old French gai. The 20thcentury sense ‘homosexual’, which first came into general use in the 1950s, can probably be traced back to the 17th-century meaning ‘sexually dissolute’.

By the early 19th century it was being applied specifically to the world of prostitution, and it seems not unlikely that male prostitutes and their male clients could have been the vector for the present-day usage. A reported 1868 song by the US female impersonator Will S. Hays was supposedly called ‘The Gay Young Clerk in the Dry Goods Store’, but it is not entirely clear what ‘gay’ is supposed to have meant here, and the earliest reliable printed record of the ‘homosexual’ sense is from 1933.

The adjective underwent a further semantic flipflop in the early 21st century, when kids’ slang commandeered it, paradoxically, for ‘sad’.
clientele (n.)youdaoicibaDictYouDict
1560s, "body of professed adherents," from French clientèle (16c.), from Latin clientela "relationship between dependent and patron, body of clients," from clientem (nominative cliens; see client). Meaning "customers, those who regularly patronize a business or professional" is from 1857, perhaps a reborrowing from French (it was used in English in italics as a foreign word from 1836).
hooker (n.)youdaoicibaDictYouDict
"prostitute," often traced to the disreputable morals of the Army of the Potomac (American Civil War) under the tenure of Gen. "Fighting Joe" Hooker (early 1863), and the word might have been popularized by this association at that time (though evidence is wanting). But it is reported to have been in use in North Carolina c. 1845 ("[I]f he comes by way of Norfolk he will find any number of pretty Hookers in the Brick row not far from French's hotel. Take my advice and touch nothing in the shape of a prostitute when you come through Raleigh, for in honest truth the clap is there of luxuriant growth." letter quoted in Norman E. Eliason, "Tarheel Talk," 1956).

One early theory traces it to Corlear's Hook, a section of New York City.
HOOKER. A resident of the Hook, i.e. a strumpet, a sailor's trull. So called from the number of houses of ill-fame frequented by sailors at the Hook (i.e. Corlear's Hook) in the city of New York. [John Russell Bartlett, "Dictionary of Americanisms," 1859]
Perhaps related to hooker "thief, pickpocket" (1560s), but most likely a reference to prostitutes hooking or snaring clients. Hook in the figurative sense of "that by which anyone is attracted or caught" is recorded from early 15c.; and hook (v.) in the figurative sense of "catch hold of and draw in" is attested from 1570s; in reference to "fishing" for a husband or a wife, it was in common use from c. 1800. All of which makes the modern sense seem a natural step. Compare French accrocheuse, raccrocheuse, common slang term for "street-walker, prostitute," literally "hooker" of men.

The family name Hooker (attested from c.975 C.E.) would mean "maker of hooks," or else refer to an agricultural laborer who used a hook (compare Old English weodhoc "weed-hook").
receptionist (n.)youdaoicibaDictYouDict
"person hired to receive clients in an office," 1900, from reception + -ist. Originally in photography studios.
Let me not forget the receptionist -- generally and preferably, a woman of refined and gentle manners, well informed and specially gifted in handling people of varied dispositions. A woman especially who knows how to handle other women, and who can make herself beloved by the children who may visit the studio. A woman, also, who in a thoroughly suave and dignified way, knows just how to handle the young man of the period so that the photographer may be glad to have his business. What a power the receptionist is when properly chosen and trained. It is not too much to say that she can both make and destroy a business, if she has the amount of discretionary power given to her in some galleries. [John A. Tennant, "Business Methods Applied in Photography," "Wilson's Photographic Magazine," October 1900]
Earlier as an adjective in theology and law (1867).