Seldom, rarely, infrequently
opposite is an adjective
The opposite of the adverb bitterly is sweetly.The word sweetly is also an adverb.
The opposite of the adverb firmly (securely) is loosely.*When used to mean forcefully or determinedly (e.g. firmly stated), the opposite could be gently, weakly, or waveringly.
The adverb "well" is the usual opposite of the adverb "badly." If "badly" is used to mean "extremely or greatly" the opposite could be "slightly." E.g. He was badly bruised./He was slightly bruised.
No, it is an adjective, the opposite of definite. The adverb form is indefinitely.
gently
Careful.
Roughly
Usually is an adverb of frequency.
Adverb does not actually have an antonym, but it might be an adjective: an adjective only modifies nouns and pronouns; an adverb modifies a verb, adjective, or another adverb.
The opposite of carefully is carelessly.Both carefully and carelessly are adverbs.
The opposite of politely is impolitely.Both politely and impolitely are adverbs.