A small part of a male cat (4)
I believe the answer is:
atom
'a small part' is the definition.
'atom' can be an answer for 'part' (I have seen 'Part of molecule ' mean 'atom' so perhaps 'part' could also mean 'atom'). I'm not certain of the 'a small' bit.
'a male cat' is the wordplay.
'male cat' becomes 'tom' (I've seen this before).
'a'+'tom'='ATOM'
'of' is the link.
Can you help me to learn more?
(Other definitions for atom that I've seen before include "Bit of make-up" , "Elementary particle" , "Part of molecule" , "Something very small perhaps" , "A mighty particle, makes huge explosion" .)