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.

1590s, "a sending abroad" (as an agent), originally of Jesuits, from Latin missionem (nominative missio) "act of sending, a dispatching; a release, a setting at liberty; discharge from service, dismissal," noun of action from past-participle stem of mittere "to release, let go; send, throw," which de Vaan traces to a PIE *m(e)ith- "to exchange, remove," also source of Sanskrit methete, mimetha "to become hostile, quarrel," Gothic in-maidjan "to change;" he writes, "From original 'exchange', the meaning developed to 'give, bestow' ... and 'let go, send'."

Meaning "an organized effort for the spread of religion or for enlightenment of a community" is by 1640s; that of "a missionary post or station" is by 1769. The diplomatic sense of "body of persons sent to a foreign land on commercial or political business" is from 1620s; in American English, sometimes "a foreign legation or embassy, the office of a foreign envoy" (1805).

General sense of "that for which one is sent or commissioned" is from 1670s; meaning "that for which a person or thing is destined" (as in man on a mission, one's mission in life) is by 1805. Meaning "dispatch of an aircraft on a military operation" (by 1929, American English) was extended to spacecraft flights (1962), hence, mission control "team on the ground responsible for directing a spacecraft and its crew" (1964). As a style of furniture, said to be imitative of furniture in the buildings of original Spanish missions to western North America, it is attested from 1900.

late 14c., "one to whom special duty is entrusted by a higher power," from Medieval Latin commissarius, from Latin commissus "entrusted," past participle of committere (see commit).

Originally especially ecclesiastical, "one who performs a bishop's duties in distant places or when he is absent;" the military sense of "official in charge of supply of food, stores, and transport" dates to late 15c. Hence "storeroom" (1882, U.S. military), especially for selling articles to persons engaged in a particular line of work,  and then "dining room in a larger facility" (1924, American English), such as a movie studio.

1610s, "action of officially consigning to the custody of the state," from commit + -ment. (Anglo-French had commettement.) Meaning "the pledging or engaging of oneself, a pledge, a promise" is attested from 1793; hence, "an obligation, an engagement" (1864).

1620s, "committing, commission" (of an offense, etc.), from commit + -al (2). Meaning "act of entrusting or giving in charge" is by 1830; that of "action of committing oneself" is from 1835. As an adjective, attested from 1884, apparently a back-formation from non-committal (q.v.).

1590s, "entrusted, delegated," past-participle adjective from commit (v.). Meaning "characterized by commitment" is from 1948.

late 15c., "person appointed to attend to any business, person to whom something is committed," from Anglo-French commite; see commit + -ee.

From 1620s as "body of persons, appointed or elected, to whom some special business or function has been entrusted;" a new formation or else an extended sense of the old noun. Related: Committeeman; committeeship.

"to again commit," in any sense (the oldest seems to be parliamentary, "send (a bill, etc.) back to committee"), 1620s, from re- "back, again" + commit (v.). Related: Recommitted; recommitting; recommitment.