There are many synonyms for the phrase "making certain" that can be used to express the idea of ensuring or confirming something. Some examples include verifying, validating, authenticating, certifying, guaranteeing, assuring, confirming, establishing, and corroborating. Each of these words conveys a sense of certainty and confidence in the fact being confirmed. Additionally, some synonyms may have additional connotations or meanings, such as "validating," which can imply that there is some sort of external standard or criteria being applied in order to ensure the accuracy of the information being confirmed. Ultimately, the choice of which synonym to use will depend on the specific context and intended meaning.