Swollen belly and oddly windy (5)
I believe the answer is:
tumid
'swollen' is the definition.
(synonyms)
'belly and oddly windy' is the wordplay.
'belly' becomes 'tum' (I've seen this before).
'and' means one lot of letters go next to another.
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternate letters of 'windy' are 'id'.
'tum'+'id'='TUMID'
(Other definitions for tumid that I've seen before include "Abnormally swollen" , "Bulging" , "Bloated" .)