late 14c.; see capital (adj.). So called because it is at the "head" of a sentence or word.

1860, "to remain clinging," 1860, especially "cling fondly to" (1871); see hang (v.) + on (adv.). As a command to be patient, wait a minute, from 1936, originally in telephone conversations.

1640s, "continue to advance," also "manage, be engaged in," from carry (v.) + on (adv.). The meaning "conduct oneself in a wild and thoughtless manner" is by 1828. Carryings-on is from 1660s as "questionable doings," from 1866 as "riotous behavior." As an adjective, carry-on, in reference to luggage that may be brought into the passenger compartment of an airliner, is attested by 1965.

1590s, "to put on," from get (v.) + on (adv.). Meaning "prosper" is from 1785; that of "to advance, make progress" is from 1798; that of "be friendly" (with) is attested by 1816.

1580s, "advance, proceed," from go (v.) + on (adv.). Meaning "behave, carry on" is from 1777; especially "to talk volubly" (1863). As an expression of derision by 1886.

Cambodian capital, literally "mountain of plenty," from Cambodian phnom "mountain, hill" + penh "full."

c. 1600 (intransitive) "to return;" 1808 (transitive) "to recover (something);" from get (v.) + back.(adv.). Meaning "retaliate" is attested by 1888.

1680s, Latin, "by the head, by heads," from per (see per) + capita "head" (see capital).

the surname (also Munroe, etc.) is said to be ultimately from the River Roe in Derry, Ireland. James Monroe (1758-1831), the fifth U.S. president, was in office from 1817 to 1825. The Monroe Doctrine (so called from 1848) is a reference to the principles of policy contained in his message to Congress on Dec. 2, 1823. Monrovia, the capital of Liberia, also was named for him at its founding in 1822 by the American Colonization Society.

In terms of national psychology, the Monroe Doctrine marked the moment when Americans no longer faced eastward across the Atlantic and turned to face westward across the continent. [Daniel Walker Howe, "What Hath God Wrought"]

1726, in on the qui vive "on the alert," from French être sur le qui vive "be on the alert," from the phrase qui voulez-vous qui vive? sentinel's challenge, "whom do you wish to live?" In other words "(long) live who?" meaning "whose side are you on?" (The answer might be Vive la France, Vive le roi, etc.). From qui (from Latin qui "who") + vive, third person singular present subjunctive of vivre, from Latin vivere "to live" (see viva).