Noun

1. A pit with no visible bottom; an abyss.
2. Hell.
   • The Bible: Revelations 9:11

     And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.

3. An endless resource or supply.
   • 1994: Asia in the Making of Europe, Donald Frederick Lach

     Lipsius was replaced at Leyden by Joseph Justus Scaliger (1540-1609), the French Protestant scholar who was known to contemporaries as "the bottomless pit of erudition."

4. A person with an apparently boundless appetite; an entity or problem which consumes seemingly endless resources.
   • 2006: The Club For Growth: Bottomless Pit (blog entry), Phillip Rodokanakis

     In other words, we will continue throwing good money after bad, trying to feed a bottomless pit's insatiable appetite for taxpayer dollars.