To exaggerate, overemphasize, overstate. An idiom. The 'over' is added unnecessarily and its usage is virtually always synonymous with a mere 'exaggerate', rather than a different word, as 'exaggerate' is not a neutral usage verb like the word 'do'. There is no threshold for the word 'exaggerate', so it is not possible to overdo. To 'overexaggerate' is to 'overoverstate'.