source: [三者三葉の西川葉子が質素にもパンの耳を食べるGIF画像｜無料GIF画像検索 GIFMAGAZINE 936886]

the tough outer part of a loaf of bread:

パンの耳, 皮,

e.g. a sandwich with the crusts cut off

e.g. I tore off several pieces of crust from the loaf.

a hard, dry scrap of bread:

(ひからびた)ひと切れのパン

e.g. a kindly old woman might give her a crust.

a layer of pastry covering a pie.

パイ, ピザの皮

a hardened layer, coating, or deposit on the surface of something, especially something soft:

かたくなった表面, かたい外皮; (傷口の)かさぶた.

e.g. a crust of snow.

the outermost layer of rock of which a planet consists, especially the part of the earth above the mantle:

〘地〙 地殻, 表層

e.g. the earth's crust

e.g. at the midocean ridge new crust is formed.

a deposit of tartrates and other substances formed in wine aged in the bottle, especially port.

form into a hard outer layer:

かたい皮, 表面になる; 表面が凍る(over).

e.g. the blisters eventually crust over.

with object cover with a hard outer layer:

…をかたい皮, 表面で覆う; かたい表面にする.

e.g. the burns crusted his cheek.

Middle English: from Old French crouste, from Latin crusta ‘rind, shell, crust’.