Spot new clerk clad in iron (7)
I believe the answer is:
freckle
'spot' is the definition.
(I know that freckle is a type of macula)
'new clerk clad in iron' is the wordplay.
'new' indicates anagramming the letters.
'clad in' is an insertion indicator.
'iron' becomes 'Fe' (chemical symbol for iron).
'clerk' with letters rearranged gives 'reckl'.
'reckl' inserted within 'fe' is 'FRECKLE'.
(Other definitions for freckle that I've seen before include "Brown mark on the skin" , "Brown spot on skin" , "Small skin spot" , "Lentigo" .)