Merriam-Webster's Collegiate® Dictionary, 11th Edition
DUSK
I. adjective
Etymology: Middle English dosk, alteration of Old English dox; akin to Latin fuscus dark brown, Old English dunn dun, dūst dust
Date: 13th century
dusky ,
II. verb
Date: 13th century
intransitive verb to become dark, transitive verb to make dark or gloomy,
III. noun
Date: 1622
the darker part of twilight especially at night, darkness or semidarkness caused by the shutting out of light