This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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v. To make dark or darker.

v. To give a darker hue to.

v. To fill with sadness; make gloomy.

v. To render vague or uncertain; obscure: The sudden drop in stock prices darkened the future for investors.

v. To tarnish or stain: a scandal that darkened the family's good name.

verb-intransitive. To become dark or darker.

v. To make dark or darker by reducing light.

v. To become dark or darker (having less light).

v. To make dark or darker in colour.

v. To become dark or darker in colour.

v. To render gloomy, dark(er) of mood

v. To become gloomy, dark of mood

v. To blind, impair eyesight

v. To be blinded, loose clear vision

v. To make dark or black; to deprive of light; to obscure.

v. To render dim; to deprive of vision.

v. To cloud, obscure, or perplex; to render less clear or intelligible.

v. To cast a gloom upon.

v. To make foul; to sully; to tarnish.

verb-intransitive. To grow or darker.

To grow dark or darker.

To grow less white or clear; assume a darker hue or appearance: as, white paper darkens with age.

To deprive of light; make dark or darker: as, to darken a room by closing the shutters.

To obscure or shut out the light of.

To render less white or clear; impart a darker hue to: as, exposure to the sun darkens the complexion.

To obscure or cloud the meaning or intelligence of; perplex; render vague or uncertain.

To render gloomy; sadden.

To deprive of vision; strike with blindness.

Hence To deprive of intellectual or spiritual light; sink in darkness or ignorance.

To sully; make foul; make less bright or lustrous.

To hide; conceal.

v. become dark or darker

v. make dark or darker

v. tarnish or stain

"As Langdon listened to the caller, Hadley watched his expression darken."

darkened    darkening    darkens   

sully    defile    tarnish    maculate    stain   

depress    sully    to darken one's door   

darkener   

sully    tarnish    darkle    cloudy    blacken   

Markan    barkan    harken   

greyer    mill-stream    moss-hung    green-lit    beadlike    fourteenth-floor    defeated    musty-smelling    broadspreading    time-darkened