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.
part of speech
The part of speech for this particular word is a noun.
The part of speech for "answer" is a noun.
adverb
what part of speech is beneath
The part of speech for "explicit" is an adjective.
The part of speech for "twirl" is a verb.
The part of speech for "unfamiliar" is an adjective.
The part of speech of "came" is a verb.
The part of speech for "lecturer" is a noun.
The part of speech for "indefinite" is an adjective.