c. 1300, "to blossom, grow" (intransitive), from Old French floriss-, stem of florir "to blossom, flower, bloom; prosper, flourish," from Latin florere "to bloom, blossom, flower," figuratively "to flourish, be prosperous," from flos "a flower" (from PIE root *bhel- (3) "to thrive, bloom"). Metaphoric sense of "thrive" is mid-14c. in English. Transitive meaning "brandish (a weapon), hold in the hand and wave about" is from late 14c. Related: Flourished; flourishing.
c. 1500, "a blossom," from flourish (v.). Meaning "an ostentatious waving of a weapon" is from 1550s; that of "excessive literary or rhetorical embellishment" is from c. 1600; in reference to decorative curves in penmanship, 1650s; as "a fanfare of trumpets," 1590s.