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1822, agent noun from dim (v.). Of mechanisms for reducing the brightness of electric lights, from 1905.
Old English dimm "dark, gloomy, obscure," from Proto-Germanic *dimbaz (cf. Old Norse dimmr, Old Frisian dim, Old High German timber "dark, black, somber"). Not known outside Germanic. Slang sense of "stupid" is from 1892. Related: Dimly; dimness.
c.1200, perhaps in Old English, from dim (adj.). Related: Dimmed; dimming.
[1910+; fr dime, perhaps influenced by deaner, earlier British tramps' term for ''shilling'']
(also dimbo, dimmo) A dime; deemer: Neither of us can make a thin dimmer (1910+)
Stupid; uncomprehending: Anybody who pays to watch these teams has to be considered just a bit dim (1892+)