It's in there because in the past it had strings attached! (5)
I believe the answer is:
rebec
'in the past it had strings attached' is the definition.
(historical string instrument)
'it's in there because' is the wordplay.
'it's in' says the answer is hidden in the clue.
'REBEC' is hidden in the letters of 'there because'.
(Other definitions for rebec that I've seen before include "Old stringed instrument" , "Mediaeval stringed instrument" , "Medieval bowed instrument" .)