Swollen belly regularly expelled wind (5)
I believe the answer is:
tumid
'swollen' is the definition.
(synonyms)
'belly regularly expelled wind' is the wordplay.
'belly' becomes 'tum' (I've seen this in another clue).
'regularly expelled' indicates alternate letters (letters removed at regular intervals).
The alternate letters of 'wind' are 'id'.
'tum'+'id'='TUMID'
(Other definitions for tumid that I've seen before include "Abnormally swollen" , "Bulging" , "Bloated" .)