Cry uncontrollably (3)
I believe the answer is:
sob
'cry uncontrollably' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for sob that I've seen before include "Blubber" , "Weep heavily, wail" , "Cry uncontrollably" , "Weep convulsively" , "Weep uncontrollably" .)