If you want to describe a person who has sunken cheeks, you can use the word "hollow-cheeked." However, if you want to use a synonym, you can consider words such as gaunt, emaciated, skeletal, or undernourished. These words all describe a person who looks thin or malnourished, and they can be used interchangeably with "hollow-cheeked." Other options include "bony," "lean," "thin," and "wasted." Whichever word you choose, make sure it accurately describes the person's appearance and conveys the right tone for your intended meaning.