bottomless
Bottomless (adj) means having no bottom, or seeming impossibly deep. Example: “The cave seemed to lead down into a bottomless pit.”
How to use bottomless
Learner’s notesIn plain EnglishHaving no limit or apparent end — used for deep pits, endless enthusiasm, or unlimited drink refills at a meal.
Fill the gap
Can you complete this real example?
The cave seemed to lead down into a _____ pit.
Etymology
From "bottom" plus "-less," first recorded in Middle English.