IPA: /ˈrʌstɪli/
KK: /ˈrʌstɪli/
In a manner that is rusty or shows signs of rust; often used to describe something that is not functioning smoothly or is out of practice.
The old door creaked rustily as it opened after years of disuse.
Rustily → It is formed from "rust" (from Old English *rust*, meaning the reddish-brown coating that forms on iron) and "-ily" (a suffix meaning in a manner). The word "rustily" means in a manner that is rusty or showing signs of rust.
Think of something that is 'rusty' — the suffix '-ily' indicates the manner, so 'rustily' describes doing something in a rusty way.