(physics) The major stable isotope of oxygen, ¹⁶₈O, having eight protons and eight neutrons; it amounts to over 99% of the element in nature

(physiology) Oxygen uptake per heartbeat at rest.

(chemistry) A thermoplastic polyether resin whose repeat unit is derived from hydroquinone

(inorganic chemistry) Any oxide of ytterbium, but especially the colourless solid Yb₂O₃ (ytterbia)

(inorganic chemistry) Any oxide of lutetium, but especially the white solid Lu₂O₃ (lutecia)

(inorganic chemistry) Any oxide of erbium, but especially the pink amorphous solid Er₂O₃ (erbia) that is used as a phosphor and in optics

(inorganic chemistry) Any oxide of terbium, but especially the white solid Tb₂O₃ (terbia)

(chemistry) The chemical compound FeO, iron oxide where iron has a valence of +2.

(chemistry) The chemical compound FeO, iron oxide where iron has a valence of +2.

(chemistry) The chemical compound Fe₂O₃, iron oxide where iron has a valence of +3.