Horse served in Bordeaux perhaps causing belly-ache (5)
I believe the answer is:
whine
'belly-ache' is the definition.
I can't judge whether this defines the answer.
'horse served in bordeaux perhaps' is the wordplay.
'horse' becomes 'h' (synonyms).
'served in' is an insertion indicator.
'bordeaux perhaps' becomes 'wine' (bordeaux is a kind of wine).
'h' going into 'wine' is 'WHINE'.
'causing' acts as a link.
Can you help me to learn more?
(Other definitions for whine that I've seen before include "Querulous complaining" , "Whimper" , "Nagging complaint" , "beef?" , "Complaining cry" .)