What part of speech is perhaps?

Answer 1

It is an adverb. That is, it modifies and/or describes the verb in the sentence. For example: 'Perhaps he will go to the store' is a modification of the verb 'go' in 'He will go to the store.' In another situation a dialogue could be posed: "Will you go to the store?" Answer: 'Perhaps.' The use of perhaps here as a stand alone response implies a modification of the verb in the question, meaning 'perhaps I will go to the store.' It would have been more obviously stated as an adverb had the response been 'Yes, shortly', or any other word that ends in '-ly', the usual ending for adverbs.

Answer 2

Perhaps is an adverb :)