Weeps convulsively (4)
I believe the answer is:
sobs
'weeps convulsively' is the definition.
('sob' can be a synonym of 'weep convulsively')
This is the entire clue.
(Other definitions for sobs that I've seen before include "Cries noisily" , "showing distress" , "cries uncontrollably" , "convulsions" , "Given evidence of distress" .)