1.nounA mechanical device, particularly an automobile, that is worn out, run down, or mechanically unreliable as indicated by noises it makes in operation.
"Mom always worried about our safety in my friend's rattletrap. I told her not to worry, as it can't go fast enough to be dangerous."
2.nounAny piece of miscellaneous equipment or junk.
3.adjectiveMechanically unreliable or in disrepair.