Adverb
In a bitter manner.
Source: Webster's dictionarybitter cold Source: Internet
it was bitterly cold Source: Internet
she complained bitterly Source: Internet
he was bitterly disappointed Source: Internet
According to the ancient sources, the two sides fought bitterly for some time. Source: Internet
According to the myth, Phaethon's brother, Cycnus, grieved bitterly and spent many days diving into the river to collect Phaethon's bones to give him a proper burial. Source: Internet