An Etymological Dictionary of Astronomy and Astrophysics

Any of various natural clays rich in ferric oxides (Fe₂O₃) and containing silica and alumina. Used as a red (→ hematite) or yellow (→ limonite) pigment.

Etymology (EN): M.E. oker, O.Fr. ocre, from L. ochra, from Gk. okhra,
from okhros “pale yellow.”

Etymology (PE): Oxrâ, loan from Gk.