Etymology
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wether (n.)
"male sheep," especially a castrated one, Old English weðer "ram," from Proto-Germanic *wethruz (source also of Old Saxon wethar, Old Norse veðr, Old High German widar, German Widder, Gothic wiþrus "lamb"), literally "yearling," from PIE root *wet- (2) "year" (source also of Sanskrit vatsah "calf," Greek etalon "yearling," Latin vitulus "calf," literally "yearling").
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bellwether (n.)
also bell-wether, "lead sheep (on whose neck a bell was hung) of a domesticated flock," mid-14c. (late 13c. in Anglo-Latin; late 12c. as a surname), from bell (n.) + wether. Figurative sense of "chief, leader" is from mid-14c.
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veal (n.)
late 14c., "calf meat as food," from Anglo-French vel, Old French veel "a calf" (12c., Modern French veau), earlier vedel, from Latin vitellus "a little calf," diminutive of vitulus "calf," perhaps originally "yearling," if related, as some think, to Sanskrit vatsah "calf," literally "yearling;" Gothic wiþrus, Old English weðer (see wether; also see veteran).
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veteran (n.)
c. 1500, "old experienced soldier," from French vétéran, from Latin veteranus "old, aged, that has been long in use," especially of soldiers; as a plural noun, "old soldiers," from vetus (genitive veteris) "old, aged, advanced in years; of a former time," as a plural noun, vetores, "men of old, forefathers," from PIE *wet-es-, from root *wet- (2) "year" (source also of Sanskrit vatsa- "year," Greek etos "year," Hittite witish "year," Old Church Slavonic vetuchu "old," Old Lithuanian vetušas "old, aged;" and compare wether). Latin vetus also is the ultimate source of Italian vecchio, French vieux, Spanish viejo. General sense of "one who has seen long service in any office or position" is attested from 1590s. The adjective first recorded 1610s.
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gelding (n.)
late 14c., "castrated animal" (especially a horse), also "a eunuch" (late 13c. as a surname), from Old Norse geldingr "wether; eunuch," from gelda "castrate" (see geld (v.)).
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mutton (n.)

"flesh of sheep used as food," c. 1300, mouton (c. 1200 as a surname), from Old French moton "mutton; ram, wether, sheep" (12c., Modern French mouton), from Medieval Latin multonem (8c.), probably [OED] from Gallo-Roman *multo-s, accusative of Celtic *multo "sheep" (source also of Old Irish molt "wether," Mid-Breton mout, Welsh mollt), which is perhaps from PIE root *mel- (1) "soft."

The same word also was borrowed into Italian as montone "a sheep," and mutton in Middle English also could mean "a sheep" (early 14c.). Transferred slang sense of "food for lust, loose women, prostitutes" (1510s) led to extensive British slang uses down to the present day for woman variously regarded as seeking lovers or as lust objects. Mutton chop "cut of mutton (usually containing a rib) for cooking" is from 1720; as a style of side whiskers from 1865, so called for the shape (narrow and prolonged at one end and rounded at the other).

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cum 

verb ("to ejaculate") and noun ("semen"), by 1973, apparently a variant of come in the sexual sense that originated in pornographic writing, perhaps first in the noun. This "experience sexual orgasm" slang meaning of come (perhaps originally come off) is attested by 1650, in "Walking In A Meadowe Greene," in a folio of "loose songs" collected by Bishop Percy.

They lay soe close together,
   they made me much to wonder;
I knew not which was wether,
   vntill I saw her vnder.
then off he came & blusht for shame
   soe soone that he had endit;
yet still shee lyes, & to him cryes,
   "Once More, & none can mend it."

It probably is older and disguised in puns, e.g. "I come, I come, sweet death, rock me a-sleep!" ["Nashe His Dildo," 1590s]

As a noun meaning "semen or other product of orgasm" come is attested by the 1920s.

The sexual cum seems to have no connection with Latin cum, the preposition meaning "with, together with, in connection with" (an archaic form of com; see com-) which English uses on occasion in names of combined parishes or benefices (such as Chorlton-cum-Hardy), in popular Latin phrases (such as cum laude), or as a combining word to indicate a dual nature or function (such as slumber party-cum-bloodbath).

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