Learner's definition of DEUCE
chiefly US, informal
a playing card that has the number two on it or two symbols on it
a situation in which each side has a score of 40
old-fashioned + informal
— used to make a question or statement more forceful
Who the deuce [=devil, hell] was that?
We've had a deuce of a time finding a good doctor. [=it has been very difficult to find a good doctor]