USA, 1826, as ‘to flog somebody like seven bells’—to give a severe beating to somebody—‘seven’ is perhaps simply an arbitrary intensifier—cf. phrases such as ‘like seven bells half-struck’ (‘with as much speed as possible’) and ‘to blow seven bells’ (‘to blow a violent gale’)
a person who covertly exercises power by personal influence over a ruler or government without having any formal authority—ascribed to William Pitt the Elder by William Godwin in 1783
1815—inner ruthlessness and determination disguised in outward gentleness and courtesy—loan translation from French ‘une main de fer dans un gant de velours’ (1814)
USA, 1969—the phrases ‘off the radar’, ‘under the radar’ and ‘below the radar’ are used of something or someone that cannot be detected—the reference is to an aircraft flying too low to be detected by a radar
UK, 1813, as ‘to blot the landscape’, meaning, of an ugly feature, to spoil the appearance of a place—also used figuratively of anything unsightly or unappealing that spoils an otherwise pleasant scene
USA, 1832—a rhetorical question calling attention to a non-sequitur or irrelevant statement or suggestion made by another person—the noun following ‘the price of’ is irrelevant to the context in which it is used
UK—1824: a slaughterhouse where old or injured horses are slaughtered and their bodies processed—1832: a notional place where ends up someone or something that is no longer useful or successful