mid-15c., "lacking form; not in accordance with the rules of formal logic," from in- (1) "not, opposite of" + formal (adj.). Meaning "irregular, unofficial, not according to rule or custom" is from c. 1600. Sense of "done without ceremony" is from 1828. Related: Informally.

1590s, from informal + -ity.

1906, American English, informal shortening of tarpaulin.

by 1987, informal. Related: Scooched; scooching.

1731, "clever, sharp, smart," shortening of acute; informal sense of "pretty" is by 1834, American English colloquial and student slang. Related: Cutely; cuteness.

informal name of the Union of Soviet Socialist Republics; in use in U.S. newspapers by October 1919.

also para-transit, "public transportation of a flexible, informal kind" (such as taxis, carpools, etc.), 1973, from para- (1) + transit.

"friendly informal gathering, a gathering for social purposes," 1870, from social (adj.). In late 17c. it meant "a companion, associate."

name of a popular science fiction film released in 1977; also the informal name for a space-based missile defense system proposed in 1983 by U.S. president Ronald Reagan.

late 15c., "speech, discourse, conversation," from talk (v.). Meaning "informal lecture or address" is from 1859. Meaning "a subject of gossip" is from 1620s (in talk of the town). Talk show first recorded 1965; talk radio is from 1985.