c. 1300, "belonging to all, owned or used jointly, general, of a public nature or character," from Old French comun "common, general, free, open, public" (9c., Modern French commun), from Latin communis "in common, public, shared by all or many; general, not specific; familiar, not pretentious." This is from a reconstructed PIE compound *ko-moin-i- "held in common," compound adjective formed from *ko- "together" + *moi-n-, suffixed form of root *mei- (1) "to change, go, move," hence literally "shared by all."

The second element of the compound also is the source of Latin munia "duties, public duties, functions," those related to munia "office." Perhaps reinforced in Old French by the Germanic form of PIE *ko-moin-i- (compare German gemein, Old English gemne "common, public, general, universal;" see mean (adj.)), which came to French via Frankish.

Used disparagingly of women and criminals since c. 1300. Meaning "pertaining equally to or proceeding equally from two or more" is from c. 1400. Meaning "usual, not exceptional, of frequent occurrence" is from late 14c. Sense of "not distinguished, belonging to the general mass" is from c. 1400; of things, "ordinary, not excellent," late 14c.

Common pleas is 13c., from Anglo-French communs plets, hearing civil actions by one subject against another as opposed to pleas of the crown. Common prayer is that done in public in unity with other worshipers; contrasted with private prayer. Common stock is attested from 1888. Common speech (late 14c.) is the vernacular, as opposed to Latin. Common good (late 14c.) translates Latin bonum publicum "the common weal." The college common room (1660s) is one to which all members have common access. 

also mean time, mid-14c., mene-time, "interim, interval between one specified time and another" (now only in in the mean time), from mean (adj.2) "middle, intermediate" + time (n.).

It is attested from late 14c. as an adverb, "during the interval (between one specified time and another)."

As a noun, properly written as two words but commonly as one, after the adverb. In the mean space "meanwhile" was in use 16c.-18c. Middle English also had therewhile (adv., conj.) "during that time, meantime."

also mean while, late 14c., "mean time, the interval between one specified period and another," from mean (adj.2) "middle, intermediate" + while (n.). From late 14c. as an adverb, "during or in a certain period of time." Properly two words as a noun but commonly written as one, after the adverb.

early 15c., cors "ordinary" (modern spelling is from late 16c.), probably adjectival use of noun cours (see course (n.)). Originally referring to rough cloth for ordinary wear, the sense of "rude, vulgar, unpolished" developed by c. 1500 and that of "obscene" by 1711.

Perhaps via the notion of "in regular or natural order," hence "common, vulgar" (compare the development of mean (adj.), also ornery from ordinary). Or it might be via the clothing sense, and the notion of "wanting fineness of texture or elegance of form." Or both, and there might be also an influence, via metathesis, of French gros (see gross (adj.)), which underwent a similar sense development. Related: Coarsely; coarseness.

"to lower in dignity, lower the standing of, debase," c. 1600, perhaps from de- "down" + mean (adj.) and modeled on debase. It is indistinguishable in some uses from obsolete demean (Middle English, from Old French demener; see demeanor) which likely influenced it and might be its ultimate source. It was much-criticized in late 19c. by purists (Fitzedward Hall, etc.), and Century Dictionary (1897) reports "the word is avoided by scrupulous writers." Related: Demeaned; demeaning.

1913, as a German word in English (the article suggests "Parish Brotherhoods" as a translation of German Gemeinschaften), from German Gemeinschaft "social relationship based on affection or kinship" (contrasted with gesellschaft), from gemein "common, general" (see mean (adj.1)) + -schaft (see -ship).

also meany, "mean-minded or stingy person," by 1927, from mean (adj.) + -y (3).

c. 1300, meninge, "sense, that which is intended to be expressed," also "act of remembering" (a sense now obsolete), verbal noun from mean (v.). Sense of "significance, import" is from 1680s.

1580s, "poorly, in an indifferent manner or condition;" 1590s, "in a low or humble degree, in a low rank in life;" c. 1600, "sordidly," later "illiberally;" from mean (adj.1) in its various later senses + -ly (2). Middle English had menelich "humbly, poorly;" Old English gemænelice "commonly, generally."

1550s, "weakness," from mean (adj.1) + -ness. Sense of "baseness, poverty, want of dignity or distinction" is from 1650s; that of "sordid illiberality, stinginess" from 1755. The Middle English senses were "fellowship; land held in common," from Old English gemænnes.