Cleavage that can be seen from beneath a woman's top (or the strip of fabric that passes for it).
Undercleavage is nice and all, but you almost have to wonder how her boobs don't slip out of her top...
by nat s. August 27, 2008
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(n.) - The bottom parts of a woman's breasts below the nipples that are visible the bottom of a very short midriff shirt or t-shirt that covers the top of her breasts.
"If that's not a deliberate display of undercleavage on that model in the Vogue photo, I don't know what is!"

-- overheard at a watercooler in Los Angeles
by PRwiz101 October 17, 2009
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