An infinitesimal particle unknown in study of the body (7)
I believe the answer is:
anatomy
'study of the body' is the definition.
'anatomy' can be an answer for 'body' (anatomy is a kind of body). I'm unsure of the 'study of the' bit.
'an infinitesimal particle unknown' is the wordplay.
'infinitesimal particle' becomes 'atom' (synonyms. I am not sure about the 'infinitesimal' bit.).
'unknown' becomes 'y' (algebra).
'an'+'atom'+'y'='ANATOMY'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for anatomy that I've seen before include "Study of bodies" , "Examining body" , "Study of the structure of animals" , "Study of animal structures" , "Study of (physical structure of) living things" .)