An Etymological Dictionary of Astronomy and Astrophysics

Any more or less hard or stiff outer covering or surface. → Earth’s crust.

Etymology (EN): M.E., from O.Fr. crouste from L. crusta “rind, crust, shell, bark;” cf. Skt. krud- “make hard, thicken;” Av. xruzdra- “hard;”
Gk. kryos “icy cold,” krystallos “ice, crystal;” Lett. kruwesis “frozen mud;” O.H.G. hrosa “ice, crust;” O.E. hruse “earth;” PIE base *kreus- “to begin to freeze, form a crust.”

Etymology (PE): Pusté, → shell.