Stretch to a bit of enamel on gatepost (8)
I believe the answer is:
elongate
'stretch' is the definition.
('elongate' can be a synonym of 'stretch')
'a bit of enamel on gatepost' is the wordplay.
'a bit of' indicates a hidden word (I've seen 'a bit' mean this (the answer is formed by a bit of the clue)).
'ELONGATE' is hidden in the letters of 'enamel on gatepost'.
'to' is the link.
(Other definitions for elongate that I've seen before include "grow further" , "Widen" , "stretcher will do!" , "Stretch, lengthen" , "Draw out" .)