late 14c., nerve, nerf, "sinew, tendon, hard cord of the body" (a sense now obsolete), also "fiber or bundle of fibers that convey the capacity to feel or move from the brain or spinal cord to the body," from Old French nerf and directly from Medieval Latin nervus "a nerve," from Latin nervus "sinew, tendon; cord, bowstring, string of a musical instrument," metathesis of pre-Latin *neuros, from PIE *(s)neu- "tendon, sinew" (source also of Sanskrit snavan- "band, sinew," Armenian neard "sinew," Greek neuron "sinew, tendon," in Galen "nerve").
The late medieval surgeons understood the nature and function of the nerves and often used nervus to denote a `nerve' in the modern sense, as well as to denote a `tendon'. There appears to have been some confusion, however, between nerves and tendons; hence, a number of instances in which nervus may be interpreted in either way or in both ways simultaneously. [Middle English Compendium]
The secondary senses developed from meaning "strength, vigor; force, energy" (c. 1600), from the "sinew" sense. Hence the non-scientific sense with reference to feeling or courage, first attested c. 1600 (as in nerves of steel, 1869) and that of "coolness in the face of danger, fortitude under trying or critical circumstances" is by 1809. The bad sense "impudence, boldness, cheek" (originally slang) is by 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 hysterical nervousness," attested by 1890, perhaps from 1792. To get on (someone's) nerves is from 1895. War of nerves "psychological warfare" is from 1915.
Old English freo "exempt from; not in bondage, acting of one's own will," also "noble; joyful," from Proto-Germanic *friaz "beloved; not in bondage" (source also of Old Frisian fri, Old Saxon vri, Old High German vri, German frei, Dutch vrij, Gothic freis "free"), from PIE *priy-a- "dear, beloved," from root *pri- "to love."
The sense evolution from "to love" to "free" is perhaps from the terms "beloved" or "friend" being applied to the free members of one's clan (as opposed to slaves; compare Latin liberi, meaning both "free persons" and "children of a family"). For the older sense in Germanic, compare Gothic frijon "to love;" Old English freod "affection, friendship, peace," friga "love," friðu "peace;" Old Norse friðr "peace, personal security; love, friendship," German Friede "peace;" Old English freo "wife;" Old Norse Frigg, name of the wife of Odin, literally "beloved" or "loving;" Middle Low German vrien "to take to wife," Dutch vrijen, German freien "to woo."
Meaning "clear of obstruction" is from mid-13c.; sense of "unrestrained in movement" is from c. 1300; of animals, "loose, at liberty, wild," late 14c. Meaning "liberal, not parsimonious" is from c. 1300. Sense of "characterized by liberty of action or expression" is from 1630s; of art, etc., "not holding strictly to rule or form," from 1813. Of nations, "not subject to foreign rule or to despotism," recorded in English from late 14c. (Free world "non-communist nations" attested from 1950 on notion of "based on principles of civil liberty.") Sense of "given without cost" is 1580s, from notion of "free of cost."
Free even to the definition of freedom, "without any hindrance that does not arise out of his own constitution." [Emerson, "The American Scholar," 1837]
Free lunch, originally offered in bars to draw in customers, by 1850, American English. Free pass on railways, etc., attested by 1850. Free speech in Britain was used of a privilege in Parliament since the time of Henry VIII. In U.S., in reference to a civil right to expression, it became a prominent phrase in the debates over the Gag Rule (1836). Free enterprise recorded from 1832; free trade is from 1823; free market from 1630s. Free will is from early 13c. Free school is from late 15c. Free association in psychology is from 1899. Free love "sexual liberation" attested from 1822 (the doctrine itself is much older), American English. Free and easy "unrestrained" is from 1690s.
also nerveracking, "causing anxiety or mental stress," 1812, from nerve (n.) + present participle of rack (v.1). Between nerve-racking and nerve-wracking (1867) this is probably the better choice as a figure of speech, but the sense of wrack (v.), though less suitable in the image, is not obviously wrong.