One who flourishes or prospers; something that causes flourishing or growth; in music, a decorative passage.
From 'flourish' (to thrive, to bloom) plus '-er' (agent noun suffix). Originally referred to someone thriving, but also adopted for ornamental musical passages that 'flourish' with decoration.
A 'flourisher' in music is a fancy ornamental run of notes—the metaphor is perfect because the notes are like flowers decorating the melody, and the original 'flourish' literally means 'to flower'!
Complete word intelligence in one call. Free tier — 50 lookups/day.