E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A cheat. The cheating game so called is played thus: A pea is put on a table, and the conjurer places three or four thimbles over it in succession, and then sets the thimbles on the table. You are asked to say under which thimble the pea is, but are sure to guess wrong, as the pea has been concealed under the mans nail.