Spots in semicolon withdrawn (4)
I believe the answer is:
loci
'spots' is the definition.
(I've seen this in another clue)
'in semicolon withdrawn' is the wordplay.
'in' says the answer is hidden in the clue.
'withdrawn' is a reversal indicator.
'icol' is hidden within 'semicolon'.
'icol' backwards is 'LOCI'.
(Other definitions for loci that I've seen before include "Particular places" , "Points where something occurs; coil (anag.)" , "Particular positions" , "sites" , "locations" .)