ichidan verb, intransitive verb
Describes metal oxidizing and corroding. Also used figuratively for skills or abilities that have declined from lack of use.
自転車を雨ざらしにしていたら、チェーンが錆びてしまった。
I left my bicycle out in the rain, and the chain rusted.
I haven't used English for a long time, so my English skills have gotten completely rusty.