IPA: /ˈɡraʊndʃiːt/
KK: /ˈɡraʊndˌʃiːt/
A waterproof sheet placed on the ground, usually under a tent, for sitting or sleeping on.
We laid out the groundsheet before setting up the tent.
Groundsheet → It is formed from "ground" (from Old English *grund*, meaning the bottom or surface of the earth) and "sheet" (from Old English *sceat*, meaning a covering or layer). The word "groundsheet" refers to a sheet that covers the ground, often used for protection or insulation.
Think of a 'sheet' that covers the 'ground' — that's what a groundsheet is, a protective layer on the earth.
No commonly confused words.