Bitter  —adj. 1 having a sharp pungent taste; not sweet. 2 causing, showing, or feeling mental pain or resentment (bitter memories). 3 a harsh; virulent (bitter animosity). B piercingly cold. —n. 1 beer flavoured with hops and tasting slightly bitter. 2 (in pl.) Liquor flavoured esp. With wormwood, used in cocktails.  to the bitter end to the very end in spite of difficulties.  bitterly adv. Bitterness n. [old english]