The synonyms of “ensure” are “guarantee”, “insure”, and “make certain”.
“Guarantee” implies a firm promise or assurance. For example, “The company guarantees the quality of its products.” It gives a sense of confidence that something will definitely happen or be achieved.
“Insure” can also mean to make certain or secure. In a more specific context, it is often associated with protecting against loss or damage. For instance, “We insured our house against fire.” But it can also be used in a broader sense to mean ensuring a particular outcome.
“Make certain” is a more straightforward way of expressing the idea of ensuring. It emphasizes taking specific actions to confirm or verify that something will occur. “We need to make certain that all the preparations are complete.”
In summary, these synonyms for “ensure” all convey the idea of taking steps to make sure that a particular result is achieved or a condition is met.