From Old English 'naegl' and PIE *h3nogh- — both body-part and fastener senses have traveled together for five millennia.
A slender, pointed metal fastener driven into wood or other materials to hold things together; also, the horny plate covering the upper surface of a finger or toe tip.
From Old English 'næġl,' meaning both 'fingernail, toenail' and 'metal spike, nail,' from Proto-Germanic *naglaz (nail, both senses), from the PIE root *h₃nogʰ- (nail, claw, hoof). The dual meaning is ancient and cross-linguistic: PIE speakers apparently perceived the structural resemblance between a fingernail (a hardened, pointed keratin plate) and a pointed metal peg used as a fastener, and the same word served for both across millennia. Latin 'unguis' (fingernail, claw), Greek 'ónyx' (nail, claw, later