#1 bitter s. [acrimonious] marked by strong resentment or cynicism; "an acrimonious dispute"; "bitter about the divorce". wn
#2 bitter s. very difficult to accept or bear; "the bitter truth"; "a bitter sorrow". wn
#3 bitter s. expressive of severe grief or regret; "shed bitter tears". wn
#4 bitter s. proceeding from or exhibiting great hostility or animosity; "a bitter struggle"; "bitter enemies". wn
#5 bitter r. [piercingly, bitterly, bitingly] extremely and sharply; "it was bitterly cold"; "bitter cold". wn
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