1. Twilight is the time just before night when the daylight has almost completely gone but when it is not completely dark.
2. Twilight is the small amount of light that there is outside just after the sun has gone down.
3. The twilight of a particular period of time is the final stages of it, when the most important events have already happened.
4. A twilight state or a twilight zone is a situation of confusion or uncertainty, which seems to exist between two states or categories.
1 & 2 - ". . . the deepening autumn twilight."
3 - "Now they both are in the twilight of their careers."
4 - "They fell into that twilight zone between Marxism and Functionalism."