Part I’m playing, hollow? (6)
I believe the answer is:
armpit
'hollow?' is the definition.
(I've seen this before)
'part i'm playing' is the wordplay.
'playing' is an anagram indicator.
'part'+'im'='partim'
'partim' with letters rearranged gives 'ARMPIT'.
(Other definitions for armpit that I've seen before include "Where to put a crutch" , "Hairy spot" , "Hollow between limb and shoulder" , "Bodily hollow" , "Hole for a limb?" .)