The word assiduously is an adverb, a word that modifies a verb, an adjective, or another adverb. Example:
He worked assiduously to complete the assignment on time.
With care and persistence
what part of speech is work
adverb
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what part of speech is beneath
With care and persistence
The part of speech for "answer" is a noun.
part of speech
The part of speech for this particular word is a noun.
He worked assiduously on his research project, devoting long hours each day to ensure it was completed to the highest standard.
adverb
what part of speech is work
what part of speech is beneath
Assiduously means with great care and diligence.
The part of speech for "indefinite" is an adjective.
The part of speech for "buried" is a verb.
The part of speech for "rapid" is an adjective.