late 14c., nerf "sinew, tendon," from Old French nerf and directly from Medieval Latin nervus "nerve," from Latin nervus "sinew, tendon; cord, bowstring," metathesis of pre-Latin *neuros, from PIE *(s)neu- "tendon, sinew" (cognates: Sanskrit snavan- "band, sinew," Armenian neard "sinew," Greek neuron "sinew, tendon," in Galen "nerve"). Sense of "fibers that convey impulses between the brain and the body" is from c.1600.Secondary senses developed from meaning "strength, vigor, energy" (c.1600), from the "sinew" sense. Hence figurative sense of "feeling, courage," first attested c.1600; that of "courage, boldness" is from 1809; bad sense "impudence, cheek" is from 1887. Latin nervus also had a figurative sense of "vigor, force, power, strength," as did Greek neuron. From the neurological sense come Nerves "condition of nervousness," attested from 1792; to get on someone's nerves, from 1895. War of nerves "psychological warfare" is from 1915.

c.1500, "to ornament with threads;" see nerve, n.. Meaning "to give strength or vigor" is from 1749. Related: Nerved; nerving.