1. most affected by rust; having the greatest amount of corrosion
Usage: superlative form of rusty
2. most out of practice; having lost the most skill through lack of use
Usage: figurative use; superlative form of rusty

Examples

• The rustiest car in the junkyard was barely recognizable.
• This old gate has the rustiest hinges I’ve ever seen.
• After years without playing, my piano skills are at their rustiest.
• He was the rustiest player on the team after his long break.
• The rustiest tools were thrown away during the garage cleanup.
• Her French is rustiest when she hasn’t practiced in months.