This is the 6719th most frequent Russian word.
rust
The Russian word "ржавчина" (rust) means a reddish-brown coating formed on iron or steel due to oxidation.
Here, 'rust' refers to the chemical process that occurs on metal surfaces when exposed to air and moisture.
Ржавчина покрыла старый металлический забор.
Rust covered the old metal fence.
In this metaphorical usage, 'rust' represents something hoarse or rough, conveying texture in sound.
Его голос звучал хрипло, как будто ржавчина в нем застряла.
His voice sounded hoarse, as if rust had gotten stuck in it.
In this idiomatic sense, 'rust' symbolizes a decline or lack of practice in a skill over time.