To supply with fuel again, or to replenish one's energy or enthusiasm after using it up.
From 're-' (again) + 'fuel' (combustible material). Fuel itself comes from Old French 'fouaille' (firewood, kindling), from Latin 'focus' (fire). The prefix system in English allowed the formation of this modern verb.
Refuel is a perfect example of how a concrete, physical word (putting gas in a car) gets borrowed as metaphor—we now 'refuel' on coffee, social time, or sleep just like our bodies were machines!
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