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The "pregnancy nubbin." It is formed when a woman is at least 6 months pregnant and her belly button, even if it was previously an innie, protrudes outward like a gigantic nipple in freezing weather.
Guy 1: So Scott's wife is pretty far along, I see.

Guy 2: She must be, she had a huge prubbin poking out of her shirt.
by Pat did it July 13, 2009
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