Lewis & Short

harmŏnĭcus, a, um, adj., = ἁρμονικός, of or belonging to agreement or harmony, harmonious, harmonic (very rare): res, Varr. L. L. 10, § 64 Müll.: harmonica ratio, quae cogit rerum naturam sibi ipsam congruere, Plin. 2, 109, 113, § 248: tinnitus, Mart. Cap. 1, § 27.