From Longman Dictionary of Contemporary Englishcome hell or high watercome hell or high waterinformal not politeALTHOUGH in spite of any problems or difficulties I decided I would get the job done by Friday, come hell or high water. → hell
Examples from the Corpus
come hell or high water• Come hell or high water, he'd never missed a race and he wasn't going to miss this one.• My father felt I should stay in my marriage come hell or high water.• I said I'd do it, so I will, come hell or high water.• I'll be there in time. Don't worry. Come hell or high water.• She'd come this far to say her piece and say it she would, come hell or high water. 