Translation guide
How to express that a skill or ability has declined due to lack of practice, or that a metal object has developed rust.
The speaker wants to say that their proficiency in something (language, sport, instrument, etc.) has worsened because they haven't used it in a while.
Literally 'one's arm dulls'. A very common and natural way to say a skill has become rusty. Used for practical skills, sports, arts, etc.
The speaker is talking about a metal object that has become covered with rust due to exposure to moisture.
The standard verb for 'to rust'. Used for iron, steel, etc.
I haven't played the piano lately, so I've gotten rusty.
Literally 'one's sense dulls'. Used when your intuition, feel, or sense for something has become less sharp.
I haven't driven in a while, so my feel for it is rusty.
Literally 'one's arm falls'. Means one's skill has declined. Similar to 腕が鈍る but slightly more direct about a drop in ability.
If you don't practice, you'll get rusty.
Simply means 'become unskilled'. Less idiomatic than the above, but straightforward. Can sound a bit blunt.
If you don't practice every day, you'll quickly get rusty.
This bicycle got rusty from being left out in the rain.
Literally 'rust attaches'. Focuses on the state of having rust on it.
The knife I hadn't used for a long time got rusty.