a long and slender projecting strip, tongue, or prong forming part of an object, as a chisel, file, or knife, and serving as a means of attachment for another part, as a handle or stock.
mid-14c., "serpent's tongue" (thought to be a stinging organ), later "sharp extension of a metal blade" (1680s), from O.N. tangi "spit of land, pointed metal tool," perhaps related to tunga "tongue" (see tongue). Figurative sense of "a sharp taste" is first recorded mid-15c.;
that of "suggestion, trace" is from 1590s. The fish (1734) so called for their spines.