Meaning

verb switch (a car's headlights) from a higher to a lower beam

verb become dim or lusterless

verb make dim or lusterless

originFrom Middle English dim, dym, from Old English dim, dimm (“dim, dark, gloomy; wretched, grievous, sad, unhappy”), from Proto-West Germanic *dimm, from Proto-Germanic *dimmaz (“dark”), from Proto-Indo-European *dʰem- (“to whisk, smoke; obscure”). Compare Faroese dimmur (“dark”), Icelandic dimmur (“dark”) and dimma (“darkness”).

Etymology from Wiktionary, CC BY-SA 3.0