the.com/tar pit

means A natural pool of thick, sticky asphalt (seeped-up petroleum) that traps and preserves anything that wanders into it, from insects to mammoths.

from 'Tar' traces back through Old English 'teoru' to a root meaning 'tree' or 'wood' — the earliest tars were sticky resins distilled from pine and other conifers for waterproofing ships and ropes. 'Pit' is just the plain old word for a hole in the ground, from Old English 'pytt,' itself borrowed long ago from Latin 'puteus,' a well. So the phrase is blunt compound honesty: a hole full of tar. The famous real-world versions, like the asphalt seeps at La Brea, formed where crude oil seeped up through the earth and the lighter parts evaporated, leaving a heavy, patient trap behind — nature building a grave that looks like a puddle.