A cat in any analysis (7)
I believe the answer is:
anatomy
'analysis' is the definition.
(anatomy is a kind of analysis)
'a cat in any' is the wordplay.
'cat' becomes 'tom' (a tom is a male cat).
'in' means one lot of letters goes inside another.
'a'+'tom'='atom'
'atom' placed within 'any' is 'ANATOMY'.
(Other definitions for anatomy that I've seen before include "Study of (physical structure of) living things" , "(Science of) physical structure of animals or plants" , "Study of body structure" , "Branch of biology" , "Scientific study of bodily structure" .)