(1):

(a.) To make foul; to sully; to tarnish.

(2):

(a.) To cast a gloom upon.

(3):

(a.) To cloud, obscure, or perplex; to render less clear or intelligible.

(4):

(a.) To render dim; to deprive of vision.

(5):

(a.) To make dark or black; to deprive of light; to obscure; as, a darkened room.

(6):

(v. i.) To grow or darker.