The word pain is a singular noun. The plural would be pains. "Mark has a pain in his foot."
Pain can also be used as a verb. "It pains him to see his wife suffering."
The prefix that means painful or difficult is"dys"
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.