Instrument carried by thespian offstage (5)
I believe the answer is:
piano
'instrument' is the definition.
(piano is a kind of instrument)
'carried by thespian offstage' is the wordplay.
'carried by' says the answer is hidden in the clue.
'PIANO' can be found hidden inside 'thespian offstage'.
(Other definitions for piano that I've seen before include "key holder" , "one of 6 [STEINWAYS]" , "Soft - musical instrument" , "Softly (mus.)" , "Musical instrument - softly, please" .)