Crustacea n.

Proto-Indo-European root meaning "to begin to freeze, form a crust."

It forms all or part of: crouton; crust; Crustacea; crustacean; cryo-; cryogenic; crystal; crystalline; crystallize; custard; encrust; Kristallnacht.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit krud- "make hard, thicken;" Avestan xruzdra- "hard;" Greek krystallos "ice, crystal," kryos "icy cold, frost;" Latin crusta "rind, crust, shell, bark;" Lettish kruwesis "frozen mud;" Old High German hrosa "ice, crust;" Old English hruse "earth;" Old Norse hroðr "scurf."

nominative neuter plural ending of certain nouns and adjectives in Latin and Greek that have been adopted into English (phenomena, data, media, criteria, etc.). It also is common in biology in Modern Latin formations of names (Mammalia, Reptilia, Crustacea).

an animal of the Crustacea, 1835; see Crustacea + -an. As an adjective, "of or pertaining to an animal of the Crustacea," 1858 (an earlier adjective was crustaceous, "pertaining to crust, crust-like," 1640s).