a prominent dark nebula in the Milky Way near the constellation Crux
usually with the: sometimes written Coal Sack
Coalsack in American English
(ˈkoulˌsæk)
noun
Astronomy
a dark nebula in the southern constellation Crux, whose dust particles obscure light from Milky Way stars behind it
Also: Coal Sack. Also called: Southern Coalsack
Word origin
[1625–35; coal + sack1]This word is first recorded in the period 1625–35. Other words that entered Englishat around the same time include: cabaret, interlock, query, specific, substratum