I am not sure I have understood your question, but I will try to give an answer, anyway.
There are some words named flat adverbs. They have the same form as their advective equivalents.
e.g. Hard can be an adjective or an adverb. It depends on the function it plays in the sentence.
He is a hard worker. - adjective
He works hard. - adverb
More flat adverbs : early, late, fast and others.
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