crust (n.)

early 14c., "hard outer part of bread," from Old French crouste (13c., Modern French croûte) and directly from Latin crusta "rind, crust, shell, bark," from PIE *krus-to- "that which has been hardened," suffixed form of root *kreus- "to begin to freeze, form a crust." Meaning "outer shell of the earth" is from 1550s.

crust (v.)

late 14c.; see crust (n.). Related: Crusted; crusting.