adjective

having a sharp, pungent taste or smell; not sweet.

raw berries have an intensely bitter flavour

sharp,acid,acidic,pungent,acrid,tart,sour,biting,harsh,unsweetened,vinegary,acetous,acerb,acerbic

noun

beer that is strongly flavoured with hops and has a bitter taste, brewed by top fermentation.

a pint of bitter