Holding a pen as a prop (4)
I believe the answer is:
stay
'a prop' is the definition.
(thesaurus)
'holding a pen' is the wordplay.
'holding' is an insertion indicator.
'pen' becomes 'sty' (sty is a kind of pen).
'a' put within 'sty' is 'STAY'.
'as' is the link.
(Other definitions for stay that I've seen before include "Check" , "Rope or wire used to support a mast" , "Supporting rope; remain" , "Visit (for the night)" , "Wait" .)