Given in to green-eyed monster? (4)
I believe the answer is:
ogre
'monster?' is the definition.
('ogre' can be a synonym of 'monster')
'given in to green-eyed' is the wordplay.
'given in' indicates the answer is hidden within the clue.
'OGRE' is hidden within 'to green eyed'.
(Other definitions for ogre that I've seen before include "Cruel and wicked person" , "Ugly giant" , "Has a monstrous role" , "Cruel, fearsome person" , "Terrifying monster" .)