brief (n.) Look up brief at Dictionary.com
from Latin breve (genitive brevis), noun derivative of adjective brevis (see brief (adj.)) which came to mean "letter, summary," specifically a letter of the pope (less ample and solemn than a bull), and thus came to mean "letter of authority," which yielded the modern, legal sense of "summary of the facts of a case" (1630s).
brief (adj.) Look up brief at Dictionary.com
late 13c., from Latin brevis (adj.) "short, low, little, shallow," from PIE *mregh-wi-, from root *mregh-u- "short" (cognates: Greek brakhys "short," Old Church Slavonic bruzeja "shallow places, shoals," Gothic gamaurgjan "to shorten").
brief (v.) Look up brief at Dictionary.com
"to give instructions or information to," 1866; originally "to instruct by a brief" (1862), from brief (n.). Related: Briefed; briefing.