Following from main exterior (4)
I believe the answer is:
next
'following' is the definition.
(synonyms)
'from main exterior' is the wordplay.
'from' indicates a hidden word.
'NEXT' is hidden in the letters of 'main exterior'.
(Other definitions for next that I've seen before include "The one following or adjacent" , "First in line" , "Nearest in space or position" , "Succeeding" , "The second cherry stone on the plate" .)