harmonize v.

late 14c., "combination of tones pleasing to the ear," from Old French harmonie, armonie "harmony," also the name of a musical instrument (12c.), from Latin harmonia, from Greek harmonia "agreement, concord of sounds," also as a proper name, the personification of music, literally "means of joining," used of ship-planks, etc., also "settled government, order," related to harmos "fastenings of a door; joint, shoulder," from PIE ar(ə)-smo-, suffixed form of root *ar- "to fit together." Modern scientific harmony, using combinations of notes to form chords, is from 16c. Sense of "agreement of feeling, concord" is from late 14c.

1772, noun of action from harmonize.