Meaning of “dim” - Learner’s Dictionary

dim

adjective uk us /dɪm/ (dimmer, dimmest)
NOT BRIGHT

not bright or clear:

He could hardly see her in the dim light.
a dim memory/recollection, etc

something you remember slightly, but not very well

STUPID UK informal

stupid:

He's nice, but a bit dim.
dimly adverb

a dimly lit room

(Definition of “dim adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)