cub

From earlier cubbe. Origin unknown. According to Pokorny, from Proto-Germanic *kubb-, from Proto-Indo-European *gup- (“round object, knoll”), from *gew- (“to bend, curve, convex, arch, vault”). Related terms include cup (cf. cupboard), coffin, cove, etc, essentially “chamber”, thus cub maybe initially derived from the sense “den”, or maybe “womb”.

A probable cognate is also found in North Germanic: dialectal Swedish kubbe, kybbe, köbbe, kibb, Danish kippe (“calf”). Also compare Icelandic and Old Norse kobbi (“seal”), Old Irish cuib (“whelp”). Compare also English cob.

Originally, the meaning was specifically "young fox", in which sense it has largely replaced English whelp.