if (one) is a day
Used to emphasize that one must be a certain age. How does he keep himself looking so young—he's got to be 60 if he's a day! A: "No, she's 24 if she's a day. She looks like a college student!" B: "I know, but she's really 38, I swear." Stu's been with the company for almost 30 years, so I bet he's 50 if he's a day.
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