Merriam-Webster's Collegiate® Dictionary, 11th Edition
BITTER
I. adjective see: bite Date: before 12th century
1. being or inducing the one of the four basic taste sensations that is peculiarly acrid, astringent, or disagreeable and suggestive of an infusion of hops, distasteful or distressing to the mind ; galling , marked by intensity or severity:, accompanied by severe pain or suffering , being relentlessly determined ; vehement , exhibiting intense animosity , d. harshly reproachful , marked by cynicism and rancor , intensely unpleasant especially in coldness or rawness , expressive of severe pain, grief, or regret , bitterish adjective bitterly adverb bitterness noun
II. noun Date: before 12th century bitter quality,
2. a usually alcoholic solution of bitter and often aromatic plant products used especially in preparing mixed drinks or as a mild tonic, a very dry heavily hopped ale,
III. transitive verb
Date: 12th century
to make bitter ,
IV. adverb
Date: 1749
to a bitter degree