"Till hell freezes over" is an idiom that suggests the idea of something that's never going to happen, or at least not anytime soon. It is a figure of speech used to express an exaggeration of persistent and unrelenting effort. Some synonyms for "Till hell freezes over" include "for eternity," "until the end of time," "forever and a day," "ad infinitum," "endlessly," "perpetually," and "without end." All of these phrases convey the same idea of something that will continue without cease. People use these synonyms in different situations to emphasize that something will not change, no matter what.