...bum died in pen (5)
I believe the answer is:
cadge
'bum' is the definition.
(I've seen this before)
'died in pen' is the wordplay.
'died' becomes 'd'.
'in' indicates putting letters inside.
'pen' becomes 'cage' (I've seen this before).
'd' going inside 'cage' is 'CADGE'.
(Other definitions for cadge that I've seen before include "Bum" , "Caged (anag.)" , "Get by begging" , "beg" , "Sponge (eg money)" .)