Is it ensure, insure, or assure?
c.1300, "belonging to all, general," 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," from PIE *ko-moin-i- "held in common," compound adjective formed from *ko- "together" + *moi-n-, suffixed form of root *mei- "change, exchange" (see mutable), hence literally "shared by all."
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- (cf. Old English gemæne "common, public, general, universal;" see mean (adj.)), which came to French via Frankish.
Used disparagingly of women and criminals since c.1300. 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 contrasted with private prayer. Common stock is attested from 1888.
late 15c., "land held in common," from common (adj.). Commons "the third estate of the English people as represented in Parliament," is from late 14c. Latin communis also served as a noun meaning "common property, state, commonwealth."
in Anglo-American property law, an area of land for use by the public. The term originated in feudal England, where the "waste," or uncultivated land, of a lord's manor could be used for pasture and firewood by his tenants. For centuries this right of commons conflicted with the lord's right to "approve" (i.e., appropriate for his own use) any of his waste, provided he left enough land to support the commoners' livestock. In the 19th century the right of approvement was in effect assumed by the government. Under modern agriculture, common pasturing became obsolete, and commons became public land used mostly for recreation.