Unsteadiness: Loss of ones equilibrium in regard to the environment. Often with a feeling of almost falling or of bumping into things. Many causes including problems in the cerebral or cerebellar portions of the brain, the spinal cord, vestibular system in the inner ear, etc. Unsteadiness is medically distinct from dizziness, lightheadedness, and vertigo. See: Dizziness, Lightheadedness, and Vertigo .