Spot new clerk clad in iron (7)
I believe the answer is:
freckle
'spot' is the definition.
(freckling is a kind of spotting)
'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' anagrammed gives 'reckl'.
'reckl' inserted into '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" .)