To spoil something by making too many improvements to it(verb)
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Use "over-egg" in a sentence
"Lepard uses wholemeal flour, which I think makes his cake unnecessarily heavy however – it's already squidgy and sodden with fruit and treacle, so why over-egg the pudding as it were?"
"The sort that can be hereditary because the females of the family are genetically predisposed to ‘over-egg the omelette’ every month."
""We have a bank of knowledge that is infinitely more urgent than any politician can understand but we have to be careful not to over-egg the rhetorical advocacy because the evidence is that, if we do, people run in the other direction.""