Merriam-Webster Collegiate Dictionary - ritornello

 noun  (plural ritornelli or -nellos)  Etymology: Italian, diminutive of ritorno return, from ritornare to return, from ri- re- + tornare to turn, from Latin, to turn on a lathe — more at turn  Date: 1675  1.  a. a short recurrent instrumental passage in a vocal composition  b. an instrumental interlude in early opera  2. a tutti passage in a concerto or rondo refrain