darken

a.

  1. To make dark or black; to deprive of light; to obscure; as, a darkened room.
  2. To render dim; to deprive of vision.
  3. To cloud, obscure, or perplex; to render less clear or intelligible.
  4. To cast a gloom upon.
  5. To make foul; to sully; to tarnish.

v. i.

  1. To grow or darker.