"the shell of a snail," 1520s, from snail (n.) + shell (n.).
Entries linking to snail-shell
snail n.
common name for a small gastropod on land or in fresh water, Middle English snail, from Old English snægl, from Proto-Germanic *snagila (source also of Old Saxon snegil, Old Norse snigill, Danish snegl, Swedish snigel, Middle High German snegel, dialectal German Schnegel, Old High German snecko, German Schnecke "snail").
This is reconstructed to be from *snog-, a variant of PIE root *sneg- "to crawl, creep; creeping thing" (see snake (n.)). The word essentially is a diminutive form of Old English snaca "snake," etymologically, "creeping thing."
Snail also formerly was used of slugs. Symbolic of slowness at least since c. 1000; snail's pace "very slow pace" is attested from c. 1400. Related: Snaily; snailish; snailing.
shell n.
"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.