as a rule, the same word can play different roles but not in the same sentence. it all depends on what the word is doing in the sentence. it could be a noun, an adjective, an adverb, a verb, etc. example: take the word 'cool'. in the sentence, "he walks cool", the word 'cool' is an adverb. in the sentence, "cool the hot dish", the word 'cool' is a verb. in the sentence, "it is a cool evening", the word 'cool' is an adjective. in the first example, "he walks cool", the word 'cool' really means 'coolly' as in "play it cool" (do not get excited; be calm).