adjective

(of a light, colour, or illuminated object) not shining brightly or clearly.

the dim glow of the fire

faint,weak,feeble,soft,pale,dull,dingy,subdued,muted,flat,lustreless,wishy-washy

verb

make or become less bright or distinct.

a smoky inferno that dimmed the sun

grow faint,grow feeble,grow dim,fade,dull,grow dark,darken,blacken,cloud over,become overcast,grow leaden,lour,become gloomy