Carapace is a scientific term for protective shell. Turtles and crabs have them, but humans don't — so we make do with bike helmets and elbow pads.

Otherwise known as outerwear for arthropods and turtles, carapace is a word you probably won't come across very often, unless you're a zoologist. But that doesn't mean you can't use it to describe someone who's a tough nut to crack. If a person has a gruff attitude meant to protect them emotionally, they've certainly enclosed themselves in a carapace of sorts.

Definitions of carapace

n hard outer covering or case of certain organisms such as arthropods and turtles

cuticle, shell, shield
the outer body wall of an insect
Type of:
large bony or horny plate as on an armadillo or turtle or the underside of a snake