verb
To make dark or darker by reducing light.
[…] they [locusts] covered the face of the whole earth, so that the land was darkened […]
So spake the Sovran voice, and Clouds began To darken all the Hill […]
To become dark or darker (having less light).
[…] the owl and the bat flew round the darkening trees:
[…] leaning at her window she watched the end of that eventful day darken over the ranges.
To get dark (referring to the sky, either in the evening or as a result of cloud).
Well, I must go in now; and you too: it darkens.
Then they passed out from the Forum, forced their way through the crowded streets, and soon were through the Porta Ratumena, outside the walls, and struck out across the Campus Martius, upon the Via Flaminia. It was rapidly darkening.
To make dark or darker in colour.
She puts on lipstick and darkens her eyebrows, which are now very scanty […]
To become dark or darker in colour.
The lovely hair had lost its rose-gold glimmer, and had darkened to rose-brown […]