nail (unguis). The horny plate covering the distal end of the terminal phalanx of each finger and toe.

to steal, or capture; “paid on the nail ,” i.e., paid ready money; nailed , taken up, or caught,—probably in allusion to the practice of nailing  bad money to the counter. We say, “as dead as a door-nail ;” most possibly because of “apt alliteration.” Shakspeare has the expression in Henry IV.

Falstaff. What! is the old king dead?

Pistol. As nail  in door.”

“Old Marley was as dead as a door-nail.

“Mind! I don't mean to say that I know of my own knowledge what there is particularly dead about a door-nail. I might have been inclined myself to regard a coffin-nail  as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile: and my unhallowed hands shall not disturb it, or the country's done for. You will, therefore, permit me to repeat, emphatically, that Marley was as dead as a door-nail.”