No. The word bitterly is an adverb.
The adverb form of the adjective bitter is bitterly--a bitterly ironic situation.Most of the time, -ly can be added to adjectives to create adverbs.
She told the truth; albeit bitterly.
No, bitterly modifies a verb making it an adverb.
The opposite of the adverb bitterly is sweetly.The word sweetly is also an adverb.
Today, he talked to me meanly and bitterly.
Bitterly is not a noun, it is an adverb, a word that describes a verb.
The president bitterly denounced the critics of his health care proposals.
Yes, "bitterly" is an adverb. It modifies a verb, adjective, or another adverb to indicate that something is done in a bitter or resentful manner. For example, "She cried bitterly when she heard the news."
The doorman complained bitterly about the noise coming from the neighbors' party late at night.
Bitter.
The word bitter is an adjective (and in another context a noun). The adverb form is bitterly.