a question mark

question mark

An unknown or uncertainty. The question mark is the grammatical symbol used to punctuate interrogative sentences (i.e. questions). I don't know why the experiment turned out this way—it's a real question mark right now. Injuries have left the team with a big question mark at the position of quarterback.
See also: mark, question
Farlex Dictionary of Idioms.

a question mark

COMMON
1. If there is a question mark over something, people do not know if it will continue to exist or what it will be like. There is a question mark over the future of old people's care as a result of the government cuts. Note: You can also say that there is a question mark hanging over something. There is a question mark hanging over the England manager's job. Note: Question mark is used in many other structures with a similar meaning. There's going to be a question mark about future US aid.
2. If there is a question mark over something, people are not sure if its quality is good. There is a question mark over the vehicle's long-term reliability. Note: You can also say that there is a question mark hanging over something. I am very pleased they have been acquitted. However it leaves a big question mark hanging over the original trial. Note: Question mark is used in many other structures with a similar meaning. There will be a question mark on his record that might stop him being promoted in the future.
See also: mark, question
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • question mark
  • punctuate
  • punctuate (something) with (something)
  • punctuate with
  • wocka wocka
  • a guinea pig
  • guinea
  • guinea pig
  • owl
  • (as) wise as an owl