rot away
1. To decompose and decay over time. I bought a bunch of fruit, but it just sat in the bowl rotting away for several weeks, until I finally just threw it all out. It's a shame to see such a grand old house go unused and rot away like that.
2. To fall off of or away from something as a result of decay or decomposition. The disease causes patients' flesh to rot away in large patches. The door completely rotted away from the frame.
rot away
to decompose; to decompose and fall away. The fallen trees rotted away and surrendered their nutrients to the soil. As the wood rotted away, it became rich humus.