adj. 1.lacking in light 2.lacking clarity or distinctness 3.made dim or less bright 4.offering little or no hope 5.slow to learn or understand dim v. 1.switch (a car's headlights) from a higher to a lower beam 2.become or make darker 3.become dim or lusterless 4.make dim or lusterless 5.make dim by comparison or conceal 6.become vague or indistinct