Definitions
1.nounThe punctuation mark "?", used at the end of a sentence to indicate a question.
2.nounA state of doubt or uncertainty."There’s a question mark over whether or not he’ll be fit for the next game."
3.nounAn enigmatic, inscrutable, or mysterious person or thing; an enigma, a riddle.
4.nounPolygonia interrogationis, a North American nymphalid butterfly with a silver mark on the underside of its hindwing resembling a question mark (sense 1).