Etymology
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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cum laude 
1872, originally at Harvard, from Medieval Latin, literally "with praise," from Latin cum "with" + laude, ablative of laus (genitive laudis) "praise" (see laud). Probably from earlier use (in Latin) at Heidelberg and other German universities.
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summa cum laude 
Latin, "with highest praise."
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magna cum laude 

designating a diploma or degree of higher standard than average, by 1856, Latin, literally "with great praise;" from magna (see magnate) + cum laude.

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come (v.)

elementary intransitive verb of motion, Old English cuman "to move with the purpose of reaching, or so as to reach, some point; to arrive by movement or progression;" also "move into view, appear, become perceptible; come to oneself, recover; arrive; assemble" (class IV strong verb; past tense cuom, com, past participle cumen), from Proto-Germanic *kwem- (source also of Old Saxon cuman, Old Frisian kuma, Middle Dutch comen, Dutch komen, Old High German queman, German kommen, Old Norse koma, Gothic qiman), from PIE root *gwa- "to go, come."

The substitution of Middle English -o- for Old English -u- was a scribal habit before minims to avoid misreading the letters in the old style handwriting, which jammed them together (see U). Modern past tense form came is Middle English, probably from Old Norse kvam, replacing Old English cuom.

Meaning "to happen, occur" is from early 12c. (come to pass "happen, occur" is from 1520s). As an invitation to action, c. 1300; as a call or appeal to a person (often in expanded forms: "come, come," "come, now"), mid-14c. Come again? as an off-hand way of asking "what did you say?" is attested by 1884. For sexual senses, see cum.

Remarkably productive with prepositions (NTC's "Dictionary of Phrasal Verbs" lists 198 combinations); consider the varied senses in come to "regain consciousness," come over "possess" (as an emotion), come at "attack," come on (interj.) "be serious," and come off "occur, have some level of success" (1864). Among other common expressions are:

To come down with "become ill with" (a disease), 1895; come in, of a radio operator, "begin speaking," 1958; come on "advance in growth or development," c. 1600; come out, of a young woman, "make a formal entry into society," 1782; come round "return to a normal state or better condition," 1841; come through "act as desired or expected," 1914; come up "arise as a subject of attention," 1844; come up with "produce, present," 1934.

To have it coming "deserve what one suffers" is from 1904. To come right down to it "get to fundamental facts" is from 1875.

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vade-mecum (n.)
"a pocket manual, handbook," 1620s, Latin, literally "go with me;" from imperative of vadere "to go" (see vamoose) + me "me" + cum "with."
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solus (adj.)
Latin, "alone" (see sole (adj.)), used in stage directions by 1590s. Masculine; the fem. is sola, but in stage directions solus typically serves for both. Also in phrases solus cum sola "alone with an unchaperoned woman" and solus cum solo "all on one's own," both literally meaning "alone with alone."
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jism (n.)
"seminal fluid, cum," 1899; earlier "energy, strength" (1842), of uncertain origin; see jazz (n.).
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triticale (n.)
hybrid cereal grass, 1952, from Modern Latin Triti(cum) "wheat" (literally "grain for threshing," from tritus, past participle of terere "to rub, thresh, grind," from PIE root *tere- (1) "to rub, turn") + (Se)cale "rye."
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quondam (adj.)

"one-time, former, having been formerly," 1580s, from earlier use as an adverb ("formerly") and a noun ("former holder" of some office or position), both 1530s, from Latin quondam (adv.) "formerly, at some time, at one time; once in a while," from quom, cum "when, as" (from PIE root *kwo-, stem of relative and interrogative pronouns) + demonstrative ending -dam. Related: Quondamship.

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