A grossly fat or slovenly woman.
In those moments when only insults will do, how good it is to turn to the inventive but unsung genius of everyday folk, whose local dialect is so often full of expressive abuse.
This one still has some small currency, mostly in Yorkshire I believe, though at one time it was widely known across a swathe of England ranging from Cumbria to Devon. That it will almost certainly be unknown to the object of your obloquy will add relish to your utterance, though it might not be too hard to work out it isn’t complimentary. It has rarely been written down outside dialect glossaries, but it did appear in 1621 in a long passage full of terms of opprobrium in The Anatomy of Melancholy by Robert Burton:
“Every lover admires his mistress, though she be ... a vast virago, or an ugly tit, a slug, a fat fustilugs”.
Many people know lug as a dialectal or regional English term for the ear (a British comedian used to exhort his audience to listen carefully with the cry “pin back your lugholes!”). If that sense were intended, the term would mean “smelly ears”, suggesting that the person didn’t wash, a plausible origin. However, the Oxford English Dictionary is sure that it’s the idea of lugging around a heavy weight that’s at the root of the matter.