in natural history, a genus of earths, slightly coherent, and composed of fine, smooth, soft, argillaceous particles, rough to the touch, and readily diffusible in water.

Ochres are of various colours, as red, yellow, blue, brown, green, &c.

OCYUMUM, in botany, a genus of the didynamia gymnosperma clas. The superior lip of the calyx is round, and the inferior is divided into four segments. There are eight species, none of them natives of Britain.