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.
opposite is an adjective
The opposite of the adverb bitterly is sweetly. The word sweetly is also an adverb.
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.
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.
No, it is not an adverb. The word violate is a noun (the opposite word, inviolate, is an adjective , as is violated).
The opposite of the adverb separately would be together, jointly, mutually, or cooperatively.
Seldom, rarely, infrequently
The opposite of carefully is carelessly. Both carefully and carelessly are adverbs.
The word early can be an adjective or an adverb. The opposite of both is the word late.
"Often" and "frequently" are antonyms of "rarely".
The opposite would be believably or credibly. However, the adverb is often used to mean unexpectedly, where the opposite would be obviously or as expected.
The opposite of neatly is messily. Another opposite is ineffectively. Clumsily can also be an opposite of neatly. Neatly, messily, ineffectively and clumsily are all adverbs.
The direct opposite is the adverb discontentedly. Other possibilities: agitatedly, disgruntledly, uneasily, unhappily.