Despite its reputation, lead is not the heaviest of the naturally occurring metals. That honor belongs to osmium (if you’re going by density) or plutonium (if you’re going by its atomic mass). But lead, traditionally used in weighted objects such as plumb lines (the Latin plumbum means “lead,” after all) has historically been the go-to element when you want to describe something as immoderately heavy.
She was all alone in her misery, and could see no way out of it. The diamonds were heavy as a load of lead within her bosom. And yet she had persevered.
— Anthony Trollope, The Eustace Diamonds, 1871
In the 16th century, the adjective leaden-footed described one who moved slowly. But when you give such a foot to a person operating a vehicle with an accelerator pedal, the image becomes one of a motorist driving at high speeds.
If you’ve been known to have a lead foot, you might want to watch out. Drivers in Lexington will soon see several city roads transition from having a 35 mph speed to a 25 mph limit.
— WKYT.com, 5 Dec. 2018