The term OPUS is used to refer to a musical composition, usually of considerable length and complexity. The crossword solutions for this term are DEI (3 letters), WORK (4 letters), RONDO (5 letters), and SONATA (6 letters). DEI stands for 'dramma per musica, ' which is an Italian opera. WORK is a musical composition that is performed by an orchestra or other large ensemble. RONDO is a musical form that is characterized by a recurring theme alternating with different episodes. Finally, SONATA is a type of musical composition that is typically written for a solo instrument or a small ensemble.