* Aggravate: To make worse or more severe.
* Exacerbate: To make worse or more severe, especially a problem or disease.
* Incite: To encourage or stir up (violent or unlawful behavior).
* Provoke: To stimulate or bring about (a reaction or emotion, typically a negative one).
* Whet: To stimulate (an appetite or desire).
Example:
* Assuage: "The doctor's kind words assuaged her fears."
* Aggravate: "His constant complaining aggravated the situation."
The best antonym for "assuage" will depend on the specific situation and the meaning you want to convey.