dim2 past tense and past participle dimmed, present participle dimming
1 [intransitive and transitive]
if a light dims, or if you dim it, it becomes less bright:
The lights in the theatre began to dim.
2 [intransitive and transitive]
if a feeling, quality etc dims or is dimmed, it grows weaker or less:
Even the rain could not dim their enthusiasm.
Hopes of a peaceful settlement have dimmed.
3 American EnglishTTC
to lower the angle of the front lights of your car, especially when someone is driving towards you [= dip British English]