rđati (Serbo-Croatian) comes from Serbo-Croatian rđa, from Proto-Slavic rъďa, from Proto-Slavic rudъ, from Proto-Balto-Slavic roudos, from Proto-Indo-European h₁rowdʰ-o-, from Proto-Indo-European h₁rewdʰ- — red.
rđati (Serbo-Croatian): to rust