Antonyms of verb brighten

1 of 2 senses of brighten

Sense 1
brighten, lighten up, lighten -- (make lighter or brighter; "The paint will brighten the room")
       Antonym of darken (Sense 3)
      => darken -- (make dark or darker; "darken a room")

Synonyms/Hypernyms (Ordered by Estimated Frequency) of verb brighten

2 senses of brighten

Sense 1
brighten, lighten up, lighten -- (make lighter or brighter; "The paint will brighten the room")
       => change, alter, modify -- (cause to change; make different; cause a transformation; "The advent of the automobile may have altered the growth pattern of the city"; "The discussion has changed my thinking about the issue")

Sense 2
clear up, clear, light up, brighten -- (become clear; "The sky cleared after the storm")