a. The diffused light from the sky during the early evening or early morning when the sun is below the horizon and its light is refracted by the earth's atmosphere.
b. The time of the day when the sun is just below the horizon, especially the period between sunset and dark.
2. Dim or diffused illumination.
3. A period or condition of decline following growth, glory, or success: in the twilight of his life.*
4. A state of ambiguity or obscurity.
[Middle English twilighte : Old English twi-, two, half; see dwo- in Indo-European roots + Old English lht, light; see light1.]
Noun 1. twilight - the time of day immediately following sunset; "he loved the twilight"; "they finished before the fall of night"
crepuscle, crepuscule, dusk, evenfall, gloaming, nightfall, fall
evening, eventide, eve - the latter part of the day (the period of decreasing daylight from late afternoon until nightfall); "he enjoyed the evening light across the lake"
night - a shortening of nightfall; "they worked from morning to night"
time of day, hour - clock time; "the hour is getting late"
2. twilight - the diffused light from the sky when the sun is below the horizon but its rays are refracted by the atmosphere of the earth
light, visible light, visible radiation - (physics) electromagnetic radiation that can produce a visual sensation; "the light was filtered through a soft glass window"
3. twilight - a condition of decline following successes; "in the twilight of the empire"
declination, decline - a condition inferior to an earlier condition; a gradual falling off from a better state
I hope my *twilight won't be another double-posted suggestion.