From Longman Dictionary of Contemporary Englishtubatu‧ba /ˈtjuːbə $ ˈtuːbə/ noun [countable] 
APMa large metal musical instrument that consists of a curved tube with a wide opening that points straight up. It produces very low sounds when you blow into it.
APMa large metal musical instrument that consists of a curved tube with a wide opening that points straight up. It produces very low sounds when you blow into it.Examples from the Corpus
tuba• He nearly went to the New York Military Academy on a tuba scholarship.• Then from 1968-70. he played bass trombone and tuba with Doe Severinson s band.• The bass trombone and tuba play the bass in octaves.• Composers have written a considerable amount of music for brass quintet consisting of two trumpets, horn, trombone, and tuba.• At first this was because he was one of the only tuba players around, but success begets success.• He taught himself to play the tuba.• The tuba, considering its size and depth, is surprisingly flexible and is capable also of a very light staccato.Origin tuba (1800-1900) Italian Latin, “large trumpet” 