The Collaborative International Dictionary
Coalsack \Coal"sack`\, n. [Coal + 2d sack.] (Astron.) Any one of the spaces in the Milky Way which are very black, owing to the nearly complete absence of stars; esp., the large space near the Southern Cross sometimes called the Black Magellanic Cloud.
Wiktionary
n. 1 A sack for carrying coal. 2 (cx astronomy English) Any of the spaces in the Milky Way which are very black, owing to the nearly complete absence of stars.
Usage examples of "coalsack".
While the Awards and Protocol officer read off the nature of the heroic deeds the noble heroes had accomplished to win that noblest of all medals, the Purple Dart with Coalsack Nebula Cluster, the Emperor rose from his throne and strode majestically forward.
Presently it would take off for Krim, Darth, and the Coalsack Stars, and if Hoddan were lucky he would be on it.
But one knew that it was going on to Lohala and Tralee and Famagusta and the Coalsack Stars.
But the Coalsack area was a spacemark good for half a sector of the galaxy.
And then they'd gone on, faithfully leaving similar letters and similar impressions on Krim, Lohala, Tralee, Famagusta, and all throughout the Coalsack stars until the stock of addressed missives ran out.