Copy after gent’s beginning to yawn (4)
I believe the answer is:
gape
'yawn' is the definition.
(I know that yawn can be written as gape)
'copy after gent's beginning' is the wordplay.
'copy' becomes 'ape' (ape can mean to copy or imitate).
'after' is a charade indicator (letters next to each other).
'beginning' says to take the initial letters.
The first letter of 'gent' is 'g'.
'ape' after 'g' is 'GAPE'.
'to' is the link.
(Other definitions for gape that I've seen before include "Look with mouth wide open" , "Stare with open mouth in wonder" , "Open-mouthed stare" , "Look in amazement or stupidity" , "wide opening" .)