One who assumes financial responsibility for another
Another view is that the underwriter impliedly undertakes to repay sums which the law may require the assured to pay towards averting losses which would, by the contract, fall upon the underwriter.
And yet in an ordinary policy of insurance there is no express provision requiring the underwriter to indemnify the assured against this liability.
The explanation seems to be that the practice of the underwriter to pay the contribution has been so uniform, and his liability has been so fully recognized, that express provisions were needless.
bloodstock underwriter for the insurance syndicate Amlin 2001.