Origin and history of nervy

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.

very common adjective suffix, "full of, covered with, or characterized by" the thing expressed by the noun, Middle English -i, from Old English -ig, from Proto-Germanic *-iga-, from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Germanic cognates include Dutch, Danish, German -ig, Gothic -egs.

It was used from 13c. with verbs (drowsy, clingy), and by 15c. with other adjectives (crispy). Chiefly with monosyllables; with more than two the effect tends to become comedic.

*

Variant forms in -y for short, common adjectives (vasty, hugy) helped poets after the loss of grammatically empty but metrically useful -e in late Middle English. Verse-writers adapted to -y forms, often artfully, as in Sackville's "The wide waste places, and the hugy plain." (and the huge plain would have been a metrical balk).

After Coleridge's criticism of it as archaic artifice, poets gave up stilly (Moore probably was last to make it work, with "Oft in the Stilly Night"), paly (which Keats and Coleridge himself had used) and the rest.

Jespersen ("Modern English Grammar," 1954) also lists bleaky (Dryden), bluey, greeny, and other color words, lanky, plumpy, stouty, and the slang rummy. Vasty survives, he writes, only in imitation of Shakespeare; cooly and moisty (Chaucer, hence Spenser) he regards as fully obsolete. But in a few cases he notes (haughty, dusky) they seem to have supplanted shorter forms.