Objects or devices designed to make something warm, like hand warmers or lap warmers, or people who warm things up.
From Old English 'wearm' (warm) plus the agent suffix -er, making 'warmer' someone or something that warms, then -s for plural.
Hand warmers work through exothermic chemical reactions—when iron oxidizes in the packets, it releases heat, which is why hikers have been using versions of them for over a century!
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