Snailshell

Part of speech: noun

Definitions

1. The coiled, hard outer casing that a snail carries on its back and retreats into for protection
2. A spiral housing made of calcium carbonate that a snail grows and lives inside throughout its life
3. The curled mineral shell belonging to a snail, which serves as both its home and a shield from predators

Etymology: "Snailshell" is about as transparent as compounds get: it joins "snail" and "shell," the hard spiral casing a snail carries on its back. Both parts are old, inherited English words, so the compound describes exactly what it names, with no borrowing or reshaping along the way. The interest lies in the second element. "Shell" originally meant any hard outer covering, the sense it keeps in "eggshell" and "nutshell," and only later narrowed to the casing of shellfish and molluscs. Pairing it with "snail" therefore spells out the creature's kind of shell, since the same word could otherwise name a tortoise's or a crab's covering.