It's a verb (and a bit of an archaic one).
sup is not a word
Sup
lysosomes sup if you go to newpoint
sup sup
Assuming you mean sup as in "what's up?", it's spelled 'sup.
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
when happy say sup
The part of speech for "explicit" is an adjective.