secondo
noun
se·con·do si-ˈkōn-(ˌ)dō 
-ˈkän-
plural secondi si-ˈkōn-(ˌ)dē
-ˈkän-
: the second part in a concerted piece
especially : the lower part (as in a piano duet)
Word History
Etymology
Italian, from secondo, adjective, second, from Latin secundus
First Known Use
1792, in the meaning defined above