To corrode means to gradually wear away or destroy something through a chemical reaction, usually involving moisture or acid. When metal corrodes, it breaks down and weakens: iron turns to rust, copper develops a green coating, and aluminum forms a white powder. A bicycle left outside in the rain might corrode over time, its chain and bolts turning rusty and rough.

Corrosion happens when certain materials react with their environment. Salt water corrodes metal faster than fresh water, which is why cars in coastal areas rust more quickly and why ship hulls need special protection. Even the Statue of Liberty has corroded: its copper surface turned from shiny brown to the famous green color we see today.

The word also describes gradual damage to non-physical things. Lies can corrode trust between friends, making a strong relationship weaken bit by bit. Constant criticism might corrode someone's confidence. In these cases, something valuable is being slowly eaten away, just like rust eats away at metal. The adjective corrosive describes anything that causes corrosion: battery acid is corrosive to metal, and harsh words can be corrosive to friendships.