Antonyms of adj radiant

1 sense of radiant

Sense 1
beaming, beamy, effulgent, radiant, refulgent -- (radiating or as if radiating light; "the beaming sun"; "the effulgent daffodils"; "a radiant sunrise"; "a refulgent sunset")

INDIRECT (VIA bright) -> dull -- (emitting or reflecting very little light; "a dull glow"; "dull silver badly in need of a polish"; "a dull sky")

Similarity of adj radiant

1 sense of radiant

Sense 1
beaming, beamy, effulgent, radiant, refulgent -- (radiating or as if radiating light; "the beaming sun"; "the effulgent daffodils"; "a radiant sunrise"; "a refulgent sunset")
       => bright (vs. dull) -- (emitting or reflecting light readily or in large amounts; "the sun was bright and hot"; "a bright sunlit room")