What part of speech is the word "not"?
Independent and official parts of speech play different roles in the language. Independent (significant) denote objects, their actions and signs. In the sentence, such words are members of the sentence.
However, in order to answer the question of what part of speech is the word “not,” one should turn to another group — the official parts of speech. They are not members of the sentence and play a service role, helping significant words to connect. The word "not" along with the word "neither" refers to the category of negative particles. The particle “not” can attach negative and positive values to words and sentences when using double negation. Thus, the sentence: “Do not rush to answer”, the particle “not” attaches a negative value, and the sentence: “A friend could not help but answer me” with two particles “not” has a positive meaning.