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1. Someone who drives very fast in their car, especially over the legal speed limit. I used to be an awful speed demon, but I got so many tickets that I nearly lost my license. OK, I know we're running late, but there's no need to be such a speed demon. I'd rather arrive alive.
2. An athlete who runs, skates, swims, cycles, etc., very fast. The team's new running back is one hell of a speed demon. The speed demon already had eight Olympic gold medals for cycling, and he finally added a Tour de France championship to his list of accolades.
3. Someone or something that performs an action much faster than is usual. I can't believe you've already read through all these reports. You're a real speed demon! Th tablet's new CPU is a speed demon, all right, but it eats through the battery like nobody's business.
1. n. a fast runner; a fast driver. Tom is a speed demon. He qualified for the Olympics.
2. n. a habitual user of methamphetamine. (Drugs.) When they are high, most speed demons don’t know what they are doing.