Final answer:
Admonition refers to a firm rebuke or a warning, commonly used to prompt someone into action or to caution them.
Step-by-step explanation:
An admonition is best defined as option 2) a firm rebuke. It means to warn or reprimand someone firmly. For example, if a professor informs the class that the exam is next week, it is not just an announcement but also serves as an admonition for students to begin their preparation. Similarly, when someone notifies their roommate that the dog is pawing at the door, it implicitly consists of an admonition to take action and let the dog out.