harmony: Ar. and P. ἁρμονία, ἡ.
in unison: adj., P. ἐμμελής; adv., P. ἐμμελῶς, ἐμμελέως; see also unanimously.
lo! here are friends to chant in unison with my lament: V. αἵδ' αὖ πάρεισι τοῖς ἐμοῖς θρηνήμασι φίλαι συνωδοί (Euripides, Orestes 132).