The term 'Bass Instrument' can refer to a variety of instruments, including the TUBA (4 letters), CELLO (5 letters), VIOL (4 letters), Oon (3 letters), and ALE (3 letters). The TUBA is a large brass instrument that produces a deep, low-pitched sound. The CELLO is a stringed instrument that is played with a bow and produces a rich, full sound. The VIOL is a bowed string instrument that is similar to the CELLO but is slightly smaller. The Oon is a type of double bass, which is a large stringed instrument that produces a deep, low-pitched sound. Finally, the ALE is a type of bass guitar, which is a stringed instrument that is played with a pick and produces a deep, low-pitched sound.