• (n.) An equal sounding; the consonance of the unison and its octaves.
E·quis'o·nance noun [ Equi- + Latin sonans , present participle of sonare to sound: confer F. équisonnance. See Sonant .] (Mus.) An equal sounding; the consonance of the unison and its octaves. 
In music, an equisonance is the consonance of the unison and its octaves.