shelly (adj.)

"hard outer covering," Middle English shel, shelle, from Old English sciell, scill, Anglian scell "seashell; eggshell," which is related to Old English scealu "shell, husk," from Proto-Germanic *skaljo "piece cut off; shell; scale" (source also of West Frisian skyl "peel, rind," Middle Low German schelle "pod, rind, egg shell," Gothic skalja "tile"), with the shared notion of "covering that splits off," from PIE root *skel- (1) "to cut." Italian scaglia "chip" is from Germanic.

Also in late Old English as "a coating or layer." The general sense of "protective outer covering of some invertebrates" is in Middle English (by c. 1400 as "house of a snail;" by 1540s in reference to a tortoise or turtle); the meaning "outer layer of a nut" (or a fruit considered as a nut) is by mid-14c. With notion of "mere exterior," hence "empty or hollow thing" by 1650s. The meaning "hollow framework" is from 1791; that of "structure for a band or orchestra" is attested from 1938. To be out of (one's) shell "emerged into life" is by 1550s.

Military use for "explosive projectile" is by 1640s, first of hand grenades, and originally in reference to the metal case in which the gunpowder and shot were mixed; the notion is of a "hollow object" filled with explosives. Hence shell shock, "traumatic reaction to the stress of battle," recorded by 1915.

Shell game "a swindle" is from 1890, from a version of the three-card game played with a pea and walnut shells.

adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic).

Originally added to nouns in Old English; it was used from 13c. with verbs, and by 15c. with other adjectives (for example crispy).

Variant forms in -y for short, common adjectives (vasty, hugy) helped poets keep step with classical feet when the grammatically empty but metrically useful -e dropped off such words in late Middle English. To replace it, by Elizabethan times, verse-writers had adapted to -y forms, and often it was done artfully, as in Sackville's "The wide waste places, and the hugy plain." Simple huge plain would have been a metrical balk.

After Coleridge's criticism of the -y forms as archaic artifice, poets gave up stilly (Moore probably was last to get away with it, 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 survived, he said, only in imitation of Shakespeare; cooly and moisty (Chaucer, hence Spenser) he regarded as fully obsolete. But in a few cases he notes (haughty, dusky) they seem to have supplanted the shorter forms.