Howl with pain (4)
I believe the answer is:
wail
'howl' is the definition.
('wail' can be a synonym of 'howl')
'with pain' is the wordplay.
'with' becomes 'w' (abbreviation).
'pain' becomes 'ail' ('ail' can be a synonym of 'pain').
'w'+'ail'='WAIL'
(Other definitions for wail that I've seen before include "Cry of lament" , "Lament loudly" , "Long cry, as of siren" , "Cry, moan" , "Cry piteously" .)