From Longman Dictionary of Contemporary Englishplumb the depths (of despair/misery/bad taste etc)plumb the depths (of despair/misery/bad taste etc)VERYto feel an unpleasant emotion in a very extreme way, or to behave in a way that is extremely unpleasant or morally bad When his wife left him, Matt plumbed the very depths of despair. That night they plumbed the depths of treachery and horror, and murdered the king as he slept. → plumb
