Remain is usually a verb, as in "Five contestants remain."
As a noun, it is usually plural (remains), as in "The cremated remains were placed in an urn."
The word "remained" is a verb. It functions as the past tense of the verb "remain," which means to stay in the same place or to continue to exist.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.
The part of speech for "rapid" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "breezy" is an adjective.
The part of speech for "buried" is a verb.