Flourish
Middle English: from Old French floriss-, lengthened stem of florir, based on Latin florere, from flos, flor- ‘a flower’. The noun senses ‘ornamental curve’ and ‘florid expression’ come from an obsolete sense of the verb, ‘adorn’ (originally with flowers).
wiktionary
From Middle English floryschen, from Old French floriss-, stem of some conjugated forms of florir (compare French fleurir), from Vulgar Latin *florīre, from Latin flōreō(“I bloom”) (and conjugation partly from flōrēscō), from flōs(“flower”). See flower + -ish.
etymonline
flourish (v.)
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.
flourish (n.)
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.
