Old English þymel "sheath or covering for the thumb," from thuma (see thumb (n.)) + instrumental suffix -el (1), used in forming names of tools (compare handle (n.)). The unetymological -b- appears mid-15c. (compare humble, nimble, etc.). Originally of leather, metal ones came into use 17c. Related: Thimbleful. Thimblerig, con game played with three thimbles and a pea or button, is attested from 1825 by this name, though references to thimble cheats, probably the same swindle, date back to 1716 (see rig (v.)).
updated on October 28, 2016