Admonish
The word "admonish" is a verb that means to warn or reprimand someone firmly, typically with the intention of correcting their behavior. It is often used when someone has done something wrong or made a mistake, and they are being cautioned or advised against repeating it.

Synonym of Admonish
The correct option to mark the synonym of "admonish" is option D, which is "caution".

Explanation
To understand why "caution" is the synonym of "admonish", let's look at the meanings of both words:

- Admonish: to warn or reprimand someone firmly, typically with the intention of correcting their behavior.
- Caution: to warn or advise someone about the potential risks, dangers, or consequences of a particular action or decision.

As we can see, both words involve giving a warning or advice to someone. In the case of "admonish," the emphasis is on correcting someone's behavior or actions, while "caution" focuses more on warning someone about the potential risks or consequences.

Therefore, "caution" is the most appropriate synonym for "admonish" as it conveys a similar meaning of giving a warning or advice to someone.

Other options provided in the question:
- Polish: This word has a completely different meaning and does not relate to the concept of warning or advising someone.
- Distribute: This word means to give out or share something among a group of people, which is not synonymous with "admonish."
- Escape: This word means to get away or break free from a dangerous or unpleasant situation, which is not synonymous with "admonish."

Hence, option D, "caution," is the correct synonym for the word "admonish."