(grammar) A word (pronoun, pronominal adjective, or adverb) implying interrogation, or used for asking a question: why, who, when, etc.

A question; an interrogation.

(grammar) Asking or denoting a question: as, an interrogative phrase, pronoun, or point.

Pertaining to inquiry; questioning

“He took on an interrogative tone of voice.”

The punctuation mark "?", used at the end of a sentence to indicate a question.

A state of doubt or uncertainty.

“There’s a question mark over whether or not he’ll be fit for the next game.”

An enigmatic, inscrutable, or mysterious person or thing; an enigma, a riddle.