Instrument certainly shorter when broken (8)
I believe the answer is:
clarinet
'instrument' is the definition.
(I know that clarinet is a type of woodwind instrument)
'certainly shorter when broken' is the wordplay.
'shorter' means to remove the last letter.
'when broken' indicates an anagram (I've seen this in other clues).
'certainly' with its final letter taken away is 'certainl'.
'certainl' with letters rearranged gives 'CLARINET'.
(Other definitions for clarinet that I've seen before include "Musical wind instrument as played by Benny Goodman" , "Music maker" , "Instrument in claret, strangely" , "Wind instrument made from Clare tin" , "Find an instrument in claret" .)