What word or phrase does your mother always say?
early 13c., from Old French unicorne, from Late Latin unicornus (Vulgate), from noun use of Latin unicornis (adj.) "having one horn," from uni- "one" (see uni-) + cornus "horn" (see horn (n.)).
The Late Latin word translates Greek monoceros, itself rendering Hebrew re'em, which was probably a kind of wild ox. According to Pliny, a creature with a horse's body, deer's head, elephant's feet, lion's tail, and one black horn two cubits long projecting from its forehead. Cf. German Einhorn, Welsh ungorn, Breton uncorn, Old Church Slavonic ino-rogu.
A mythical animal resembling a small horse but with a long, straight horn growing out of its forehead. Often it was described as having the legs of a deer and the tail of a lion. Some sources claim it was visible only to virgins.
described as an animal of great ferocity and strength (Num. 23:22, R.V., "wild ox," marg., "ox-antelope;" 24:8; Isa. 34:7, R.V., "wild oxen"), and untamable (Job 39:9). It was in reality a two-horned animal; but the exact reference of the word so rendered (reem) is doubtful. Some have supposed it to be the buffalo; others, the white antelope, called by the Arabs rim. Most probably, however, the word denotes the Bos primigenius ("primitive ox"), which is now extinct all over the world. This was the auerochs of the Germans, and the urus described by Caesar (Gal. Bel., vi.28) as inhabiting the Hercynian forest. The word thus rendered has been found in an Assyrian inscription written over the wild ox or bison, which some also suppose to be the animal intended (comp. Deut. 33:17; Ps. 22:21; 29:6; 92:10).