To have the black ox tread on one's foot

Ox Ox ([o^]ks), n.; pl. {Oxen}. [AS. oxa; akin to D. os. G. ochs, ochse, OHG. ohso, Icel. oxi, Sw. & Dan. oxe, Goth. a['u]hsa, Skr. ukshan ox, bull; cf. Skr. uksh to sprinkle. [root]214. Cf. {Humid}, {Aurochs}.] (Zo["o]l.) The male of bovine quadrupeds, especially the domestic animal when castrated and grown to its full size, or nearly so. The word is also applied, as a general name, to any species of bovine animals, male and female. [1913 Webster]

All sheep and oxen, yea, and the beasts of the field. --Ps. viii. 7. [1913 Webster]

Note: The castrated male is called a steer until it attains its full growth, and then, an ox; but if castrated somewhat late in life, it is called a stag. The male, not castrated, is called a bull. These distinctions are well established in regard to domestic animals of this genus. When wild animals of this kind are spoken of, ox is often applied both to the male and the female. The name ox is never applied to the individual cow, or female, of the domestic kind. Oxen may comprehend both the male and the female. [1913 Webster]

{Grunting ox} (Zo["o]l.), the yak.

{Indian ox} (Zo["o]l.), the zebu.

{Javan ox} (Zo["o]l.), the banteng.

{Musk ox}. (Zo["o]l.) See under {Musk}.

{Ox bile}. See {Ox gall}, below.

{Ox gall}, the fresh gall of the domestic ox; -- used in the arts and in medicine.

{Ox pith}, ox marrow. [Obs.] --Marston.

{Ox ray} (Zo["o]l.), a very large ray ({Dicerobatis Giorn[ae]}) of Southern Europe. It has a hornlike organ projecting forward from each pectoral fin. It sometimes becomes twenty feet long and twenty-eight feet broad, and weighs over a ton. Called also {sea devil}.

{To have the black ox tread on one's foot}, to be unfortunate; to know what sorrow is (because black oxen were sacrificed to Pluto). --Leigh Hunt. [1913 Webster]