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).