Stomach is tender in Accident and Emergency (5)
I believe the answer is:
abide
'stomach' is the definition.
(synonyms)
'tender in accident and emergency' is the wordplay.
'tender' becomes 'bid' (synonyms).
'in' is an insertion indicator.
'accident and emergency' becomes 'AE' (A and E department at a hospital).
'bid' placed inside 'ae' is 'ABIDE'.
'is' acts as a link.
(Other definitions for abide that I've seen before include "Remain - tolerate" , "Tolerate; live" , "Stomach" , "Tolerate - dwell" , "Accept" .)