aeruginous

The story

1. Latin · derived fromaerūginōsus“rusty”
2. Middle French · derived fromerugineux“verdigris-colored”
3. Medieval Latin · derived fromaerūginōsus“rust-colored”
4. English todayaeruginous

From Medieval Latin aerūginōsus (“rust-colored”) directly and via Middle French erugineux (“verdigris-colored”), from Latin aerūginōsus (“rusty”), from aerūgō (“rust”) + -ōsus (“-ose: forming adjectives”), from aes (“copper, bronze, brass”) + -ūgō (“forming nouns related to thin coatings or coverings”).