word-forming element usually meaning "with, together," from Latin com, archaic form of classical Latin cum "together, together with, in combination," from PIE *kom- "beside, near, by, with" (compare Old English ge-, German ge-). The prefix in Latin sometimes was used as an intensive.

Before vowels and aspirates, it is reduced to co-; before -g-, it is assimilated to cog- or con-; before -l-, assimilated to col-; before -r-, assimilated to cor-; before -c-, -d-, -j-, -n-, -q-, -s-, -t-, and -v-, it is assimilated to con-, which was so frequent that it often was used as the normal form.

also noncom, by 1817, short for non-commissioned(officer).

The "non-coms" — non-commissioned, meaning, not non compos; though evil-minded high privates declare it might well mean that — have assigned to them an upper cabin, with staterooms, over the quarters of the officers, in the after-part of the ship. [James K. Hosmer, "The Color-Guard," Boston, 1864]

1620s, "to mix together, blend" (intransitive), from com- + mingle. Also see comingle. Transitive sense attested by 1840. Related: Commingled; commingling.

before vowels coen-, word-forming element meaning "common," from Latinized form of Greek koinos "common, public, shared, general, ordinary," from PIE *kom "beside, near, by, with" (see com-).

"fellow-countryman, inhabitant of the same country with another," 1610s, from French compatriote (16c.), from Latin compatriota, from com "with, together" (see com-) + patriota "countryman" (see patriot).

1560s, "mutual relation, interdependence, interconnection," from French corrélation, from cor- "together" (see com-) + relation (see relation). Meaning "action of bringing into orderly connection" is by 1879.

1915, from con-, assimilated form of Latin com "with, together" (see com-) + urbs "city" (see urban (adj.)) + noun ending -ation. Coined by Scottish biologist and urban planner Patrick Geddes in "Cities in Evolution."

"one who is the peer or equal of another," also "a close friend, companion," late 14c., from Old French compere, an appellation of friendly greeting, "friend, brother," from com- "with" (see com-) + second element from Latin parem "equal" (see par (n.)).

"an agreement or contract between two or more parties," 1590s, from Latin compactum "agreement," noun use of neuter past participle of compacisci "come to agreement," from com "with, together" (see com-) + pacisci "to covenant, contract" (from PIE root *pag- "to fasten").

"companion," 1834, American English, from Spanish compadre "godfather," hence "benefactor, friend," from Medieval Latin compater, from com "with, together" (see com-) + pater "father" (see father (n.). Compare compere, compeer, also gossip (n.).