Which one is the odd one out?

CLARION

The correct answer is: CLARION

The other options are all types of early musical instruments:

-> SPINET: a type of harpsichord

-> CLAVICHORD: a type of early keyboard instrument

-> HARPSICHORD: a type of stringed instrument

CLARION, on the other hand, is a type of trumpet or horn, which is not an early musical instrument in the same category as the others.