underflowPronunciation: /ˈʌndəfləʊ/Definition of underflow noun 1an undercurrent: the powerful underflow around the wreck a horizontal flow of water through the ground, especially beneath a riverbed. 2 [mass noun] Computing the generation of a number that is too small to be represented in the device meant to store it. underflow in other Oxford dictionaries Definition of underflow in the US English dictionary