rust
UK[rʌst]US[rʌst]
n
A reddish-brown substance that forms on iron or steel when it gets wet.
v
To become covered with rust.
v
To become worse because of lack of use.
Etymology
The word 'rust' descends directly from the Old English noun 'rūst', which meant the reddish coating on iron. This Old English term is cognate with Old Norse 'rust' and is traced back to the Proto-Germanic root 'rusta-', signifying the same phenomenon. The core concept of corrosion, specifically the reddish oxidation of iron, has remained remarkably stable from its ancient Germanic origins to its modern English usage. The verb sense, meaning to deteriorate through disuse, is a later figurative extension of the physical process of metal decaying.
Analysis
This is a simplex word of Old English origin. The form 'rust' functions as a complete lexical root.
Examples
The old bicycle was covered in a thick layer of rust.
If you leave your tools outside, they will rust.
My language skills have started to rust from lack of practice.