Unicorn in Fausset's Bible Dictionary

reem. In Deuteronomy 33:17, "his (Joseph's) horns are like the horns of an unicorn" (so margin rightly, not "unicorns"); "the ten thousands of Ephraim and the thousands of Manasseh," two tribes sprung from the one Joseph, are the two horns from one head. Therefore the unicorn was not as is represented a one-horned animal, but some species of urns or wild ox. The rhinoceros does not "skip" as the young unicorn is represented to do (Psalm 29:6). The unicorn's characteristics are: (1) great strength, Numbers 23:22; Job 39:11; (2) two horns, Deuteronomy 33:17; (3) fierceness, Psalm 22:21; (4) untameableness, Job 39:9-11, where the unicorn, probably the wild bison, buffalo, ox, or urus (now only found in Lithuania, but then spread over northern temperate climes, Bashan, etc., and in the Hercynian forest, described by Caesar as almost the size of an elephant, fierce, sparing neither man nor beast) stands in contrast to the tame ox used in plowing, Job 39:11-12; (5) playfulness of its young, Psalm 29:6; (6) association with "bullocks and bulls" for sacrifice, Isaiah 34:6-7; (7) lifting up the horn, Psalm 92:10, as bovine animals lower the head and toss up the horn.

Link: https://bible-history.com/faussets/U/Unicorn/