A man involved in no branch of science (7)
I believe the answer is:
anatomy
'branch of science' is the definition.
'anatomy' can be an answer for 'science' (anatomy is a kind of science). I'm unsure of the 'branch of' bit.
'a man involved in no' is the wordplay.
'man' becomes 'tom' (man's name).
'involved in' is an insertion indicator.
'no' becomes 'nay' (archaic form of 'no').
'tom' going into 'nay' is 'natomy'.
'a'+'natomy'='ANATOMY'
Can you help me to learn more?
(Other definitions for anatomy that I've seen before include "Bodily structure of animal or plant" , "Study of the structure of animals" , "The scientific study of bodily structures" , "Study of body structure" , "Study of animal structures" .)