1 [mass noun] the soft glowing light from the sky when the sun is below the horizon, caused by the reflection of the sun’s rays from the atmosphere:she looked out on the beautiful twilight
the period of the evening when twilight is visible, between daylight and darkness:a pleasant walk in the woods at twilight
2 [in singular] a period or state of obscurity, ambiguity, or gradual decline:he was in the twilight of his career [as modifier]:a twilight world of secrecy