Able to resist or withstand high temperatures without damage; resistant to heat.
Compound of 'heat' and 'proof' (from Old French 'prueve,' originally meaning test but evolved to mean resistant or impervious to). The '-proof' suffix is highly productive in modern English.
The '-proof' suffix is relatively recent in its productive form—we didn't say 'fireproof' until the 18th century, but now it's everywhere: waterproof, dustproof, soundproof, even 'foolproof.' It's a modern way of saying 'resistant to' or 'testing against.'
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