Over the side of a ship into the water, or to do something excessively without restraint.
Compound of 'over' and 'board' (side of a ship); the literal nautical meaning developed first, then the figurative meaning 'to excess' emerged, as in the phrase 'go overboard' meaning to take things too far.
The phrase 'going overboard' became so popular that the original maritime danger is almost forgotten—yet sailors genuinely feared falling overboard because rescue was nearly impossible before modern technology!
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