rusty
adj.adj. less skilled at something than you used to be because you have not practiced for a long time. You use this when you need to refresh your memory or skills.
adj. describing a skill or knowledge that has declined due to lack of practice or use. Often used figuratively to describe mental or physical performance rather than physical corrosion.
My French is a bit rusty because I haven't spoken it in years.
I tried to play the piano after a decade away, but my fingers felt incredibly rusty and slow.
While the veteran pilot's technical knowledge remained intact, his manual handling skills were noticeably rusty during the emergency simulation after his six-month sabbatical.
Commonly used with 'a bit' or 'a little' to soften the description of one's declining skills.