contrabassoon kon truh ba soohn n the bassoon that is the largest instrument in the oboe family Usage(s) When Sensale is not playing the contrabassoon he spends much of his time whittling the cigaret-shaped reeds of his 25-lb. You say the contrabassoon plays lower than the piano, while the reverse is true. Low B flat, the lowest tone in music that is not just a grunt, is sounded in orchestras by the contrabassoon or the contrabass tuba. Synonym(s) contrafagotto double bassoon