Sesquialter \Ses`qui*al"ter\, a. Sesquialteral. Sesquialter \Ses`qui*al"ter\, Sesquialtera \Ses`qui*al"ter*a\, n. [NL. sesquialtera.] (Mus.) A stop on the organ, containing several ranks of pipes which re["e]nforce some of the high harmonics of the ground tone, and make the sound more brilliant.