Real Dictionary

I doubt it
convention: You say I doubt it as a response to a question or statement about something that you think is untrue or unlikely.

I doubt it in American English
noun: a card game, the object of which is to rid oneself of all cards, in which the first player places aces face down on the table and the others follow, in turn, with cards of the next lower rank, adding at will other cards, except that if such deception is s