Explanation:

Certainly! Let's explore the meaning of "ensure" and its relevant synonyms:

- Ensure: Means to make certain something will occur.

- Option 1: Tasteless: Lacking flavor or not having aesthetic taste. Not related to "ensure."

- Option 2: Confirm: Means to gurarntee. 

- Option 3: Commonness: Refers to the state of being common. Not related to "ensure."

- Option 4: Insecure: Lacking confidence. Opposite of ensuring something.

The correct synonym for "ensure" among the given options is confirm.