• (n.) A lesser third, having its terms as 6 to 5; a hemiditone.
Sem`i·di'tone` noun [ Prefix semi- + ditone : confer Italian semiditono . Confer Hemiditone .] (Gr. Mus.) A lesser third, having its terms as 6 to 5; a hemiditone. [ R.] 
In music a semiditone is a lesser third, having its terms as 6 to 5.