Counter tenor \Coun"ter ten`or\ (t?n`?r). [OF. contreteneur. Cf. {Contratenor}, and see {Tenor} a part in music.] (Mus.) One of the middle parts in music, between the tenor and the treble; high tenor. {Counter-tenor clef} (Mus.), the C clef when placed on the third line; -- also called {alto clef}.