When we want to express certainty or assurance about something, we often use the phrase "more sure thing." However, there are many synonyms that can be used in place of this phrase. Some alternatives include "certainty," "concrete," "definite," "secure," "unchanging," "unquestionable," and "guaranteed." Each of these words can convey a sense of conviction and confidence, and can be used to emphasize the reliability of a particular statement or claim. Using synonyms for "more sure thing" can add variety and specificity to your writing or speech, and help you to express your thoughts and ideas with greater clarity and precision.