/ dʌsk; NAmE / noun
[ U ] the time of day when the light has almost gone, but it is not yet dark
SYN twilight :
The street lights go on at dusk .
—compare dawn
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WORD ORIGIN
Old English dox dark, swarthy and doxian darken in colour , of Germanic origin; related to Old High German tusin darkish; compare with dun . The noun dates from the early 17th cent. The change in form from -x to -sk occurred in Middle English .