When we talk about a "bitter cup," we generally mean a difficult or unpleasant experience. There are a variety of synonyms that can be used to convey similar meanings. For example, you might describe a difficult situation as a "hardship," a "trial," or a "struggle." Similarly, an unpleasant experience might be described as a "calamity," a "misfortune," or a "tragedy." Other related concepts could include "suffering," "adversity," or "distress." Each of these words expresses a different shade of meaning, and could be used to capture nuances in the specific type of difficulty or unpleasantness being experienced.