c. 1300, citisein (fem. citeseine) "inhabitant of a city or town," from Anglo-French citesein, citezein "city-dweller, town-dweller, citizen" (Old French citeien, 12c., Modern French citoyen), from cite (see city) + -ain (see -ian). According to Middle English Compendium, the -s-/-z- in Anglo-French presumably replaced an earlier *-th-.Old English words were burhsittend and ceasterware.
Sense of "freeman or inhabitant of a country, member of the state or nation, not an alien" is late 14c. Meaning "private person" (as opposed to a civil officer or soldier) is from c. 1600. As a title, 1795, from French: During the French Revolution, citoyen was used as a republican alternative to Monsieur.
Citizen's arrest, one carried out by a private person, without a warrant, allowable in certain cases, is recorded from 1941; citizen's band (radio) from 1947. Citizen of the world (late 15c.) translates Latin civem totius mundi, Greek kosmopolites.
He is not a citizen who is not disposed to respect the laws and to obey the civil magistrate; and he is certainly not a good citizen who does not wish to promote, by every means in his power, the welfare of the whole society of his fellow-citizens. [Adam Smith, "Theory of Moral Sentiments"]
"inhabitant of a city," colloquial shortening of citizen, 1640s; especially "a London cockney," as contrasted to a country man or a gentleman, usually with some measure of opprobrium (Johnson defines it as "A pert low townsman; a pragmatical trader").
late 14c., "status of a citizen," from Old French civilite (14c.), from Latin civilis "relating to a citizen, relating to public life, befitting a citizen; popular, affable, courteous" (see civil). Later especially "good citizenship" (1530s). Also "state of being civilized" (1540s); "behavior proper to civilized persons" (1560s).
"man of the world; citizen of the world, one who is cosmopolitan in ideas or life," 1610s, from Latinized form of Greek kosmopolites "citizen of the world," from kosmos "world" (see cosmos) + polites "citizen," from polis "city" (see polis). In common use 17c. in a neutral sense; it faded in 18c. but was revived from c. 1800 with a tinge of reproachfulness (opposed to patriot).
1540s, "pertaining to a city or citizenship," originally in civic crown (Latin corona civica), a chaplet of oak leaves awarded to one who saved the life of a fellow citizen in battle, from Latin civicus "of a citizen," adjectival derivative of civis "townsman" (see city). Sense of "having to do with citizens" is from 1790.