principle of equivalence: (physics) the principle that an observer has no way of distinguishing whether his laboratory is in a uniform gravitational field or is in an accelerated frame of reference
principle: a rule or law concerning a natural phenomenon or the function of a complex system
tabes dorsalis: syphilis of the spinal cord characterized by degeneration of sensory neurons and stabbing pains in the trunk and legs and unsteady gait and incontinence and impotence