A support that goes against the back of something, like a chair or vehicle seat, to hold your back in place.
Compound of 'back' (Old English 'bæc', rear side) and 'rest' (Old English 'ræst', a place to lean). Formed in English as a practical descriptor for furniture components.
The backrest is such a simple invention, but its existence completely changed how humans sit—before proper backrests, people either leaned against walls or sat in uncomfortable upright positions for hours. That single innovation probably improved posture and reduced back pain for billions of people.
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