question-mark

noun

1. 1

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

2. 2

   A state of doubt or uncertainty.

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

3. 3

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

4. 4

   Polygonia interrogationis, a North American nymphalid butterfly with a silver mark on the underside of its hindwing resembling a question mark (sense 1).