Following from main exterior (4)
I believe the answer is:
next
'following' is the definition.
(synonyms)
'from main exterior' is the wordplay.
'from' says the answer is hidden in the clue.
'NEXT' can be found hidden inside '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" .)