The Collaborative International Dictionary of English v.0.48:

Concertante \Con`cer*tan"te\ (?; It. ?), n. [It., orig p. pr. of
   concertare to form or perform a concert. See Concert.]
   (Mus.)
   A concert for two or more principal instruments, with
   orchestral accompaniment. Also adjectively; as, concertante
   parts.
   [1913 Webster]