Found in The Abbey on old musical instrument (5)
I believe the answer is:
cello
'musical instrument' is the definition.
(cello is a kind of musical instrument)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cello that I've seen before include "It's bigger than a viola, but smaller than a double bass" , "String quartet instrument" , "Musical instrument like large violin held between knees" , "10 [INSTRUMENT]" , "has strings attached" .)