From Longman Dictionary of Contemporary Englishquestion markˈquestion mark ●●○ noun [countable] 1 SLAthe mark (?) that is used at the end of a question2 → there is a question mark over something/a question mark hangs over something
Examples from the Corpus
question mark• Why did it have a question mark?• But when he looked at me, that furrow of care between his eyes turned into a question mark.• They grew up in the Depression, when the certainty of a meal was a question mark.• Another question mark will be how the offering apportions the values of Wired, HotWired and HardWired.• In the middle was a sharp little machine self-portrait, with a blinking question mark inside on the screen inside the screen.• If the bolts were responsible, then a further question mark will hang over the future of the industry.• All the mirrors grew convex, she fingered the globe in its pregnant question mark.From Longman Business Dictionaryquestion markˈquestion mark noun [countable] a question mark over if there is a question mark over something, there is a possibility that it will not be successful or will not continue to existThere is a big question mark over the bank’s long-term future. 