Jamieson, Fausset and Brown on Job 39:9

9. unicorn--Pliny [Natural History, 8.21], mentions such an animal; its figure is found depicted in the ruins of Persepolis. The Hebrew reem conveys the idea of loftiness and power (compare Ramah; Indian, Ram; Latin, Roma). The rhinoceros was perhaps the original type of the unicorn. The Arab rim is a two-horned animal. Sometimes "unicorn" or reem is a mere poetical symbol or abstraction; but the buffalo is the animal referred to here, from the contrast to the tame ox, used in ploughing (Job 39:10, 12).

abide--literally, "pass the night."

crib--(Is 1:3).