crust
n. C / Un. the hard outer layer of something, like a loaf of bread or the surface of the Earth. You can also use it to describe any thin, dry covering on top of a softer middle.
n. the hardened exterior layer of a substance, such as the outermost solid shell of a rocky planet or the baked surface of bread. Often refers to a thin, brittle covering that protects or encloses a softer interior.
The bread has a thick, crunchy crust.
Geologists study the Earth's crust to understand how tectonic plates move and cause earthquakes.
The chef carefully brushed the pastry with egg wash to ensure the crust would achieve a deep golden hue and a delicate, flaky texture during the baking process.
From Middle English cruste, from Anglo-Norman and Old French cruste, from Latin crusta (“hard outer covering”), from Proto-Indo-European krustós (“hardened”), from krews- (“to form a crust, begin to freeze”), related to Old Norse hroðr (“scurf”), Old English hruse (“earth”), Old High German hrosa (“crust, ice”), Latvian kruvesis (“frozen mud”), Ancient Greek κρύος (krúos, “frost, icy cold”), κρύσταλλος (krústallos, “crystal, ice”), Avestan 𐬑𐬭𐬎𐬰𐬛𐬭𐬀- (xruzdra-, “hard”), Sanskrit क्रूड् (krūḍ, “thicken, make hard”).
Countable when referring to specific types or layers; uncountable when referring to the substance in general.