ржа́вчинный (Russian) comes from Russian -ый, from Church Slavonic -ыи, from Proto-Slavic jь, from Proto-Balto-Slavic iś, from Old Polish ić, from Proto-Slavic jьti, from Proto-Balto-Slavic eitei, from Proto-Indo-European h₁éyti — to go.
ржа́вчинный (Russian): rust, related to rust