"bitterly" in the adverb sense
1. bitterly
with bitterness in a resentful manner
"she complained bitterly"
2. bitterly
indicating something hard to accept
"he was bitterly disappointed"
3. piercingly, bitterly, bitingly, bitter
extremely and sharply
"it was bitterly cold"
"bitter cold"
Source: WordNet® (An amazing lexical database of English)
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