William Cobbett, who I believe coined the useful expression “tax-eaters” for those who live parasitically on the political system, also coined an expression for the London of his time (which, though it contained a big cohort of tax-eaters, was considerably more commercial than today’s greater Washington, D.C., region). He called it “the Great Wen.”
The OED gives the meanings of “wen” as: “a lump or protuberance on the body . . . a sebaceous cyctic tumor . . . the swelling on the throat characteristic of goiter . . . an excrescence or tumor on the body of a horse . . . an excrescence on a tree (‘one old oak . . . had a kind of excrescence or wen upon it . . . its semicircle was thirty-two feet’) . . .
That last usage is listed as Obs. by the OED but it was current in mid-20th-century England, at least in my dialect area, and that was how I took it: as one of those unsightly tumor-type growths you see on old trees.
It’s one of those images that stays with you.