The chiefly British term for a sleeper car, in other words, a car that has very high performance, but looks as sensible, unassuming, and everyday-looking as any suburban sedan coming to pick up the kids from school.

The name "Q-car" comes from the "Q-boats" or "Q-ships" used by the British forces in World War I & World War II that were armed military ships, but disguised to look like a civilian passenger or shipping vessel. Compare to ricer, a car that has all kinds of tacky, superficial, and stupid exterior modifications, but usually an underpowered 4-cylinder engine (all show, no go).
See that Ford Five Hundred that beat that riced-out Civic? Definitely a q-car.
by RDS February 3, 2007
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