iron oxide

/AY1 ER0 N AA0 K S AY0 D/
noun
  1. 1

    The compound obtained by the reaction of oxygen on iron. Either iron(II) oxide (old term ferrous oxide, chemical formula FeO) or iron(III) oxide (old term ferric oxide, chemical formula Fe2O3). Generally known as rust when hydrated.

Source: https://en.wiktionary.org/wiki/iron%20oxide