Stop a particular activity for the rest of the day, as in It's past five o'clock so let's call it a day. Similarly, call it a night means “to stop something for the rest of the night,” as in One more hand of bridge and then let's call it a night. The original phrase was call it half a day, first recorded in 1838, which referred to leaving one's place of employment before the work day was over. The first recorded use of call it a day was in 1919, and of call it a night in 1938. Also see call it quits.