To encrust means to cover something with a hard layer or coating, like a crust forms on bread. When something becomes encrusted, it gets covered with a layer of material that hardens and sticks to the surface.

Barnacles encrust the hull of a ship that sits in the ocean too long, building up layer after layer until the bottom looks bumpy and rough. Salt can encrust the edges of a glass if you leave a drink sitting out for days. A treasure chest pulled from the ocean floor might be encrusted with coral, shells, and minerals that have built up over decades underwater.

Jewelers sometimes encrust crowns and tiaras with precious gems, carefully setting diamonds or rubies into the metal so they cover the surface. In this case, encrusted can mean something beautiful rather than something that accumulated naturally, but the idea is the same: a surface covered with a layer of material.

The word usually suggests that the covering formed gradually over time or was carefully applied, and that it's now firmly attached to whatever it covers. Whether it's dirt encrusting old coins or jewels encrusting a royal scepter, the coating isn't coming off easily.