Words:
* Frowning: This is the most common and direct way to describe a stern expression.
* Scowling: This implies a more intense and angry frown.
* Grim: This word suggests a serious and forbidding expression.
* Solemn: This implies a serious and formal expression.
* Grave: This conveys a serious and concerned expression, often with a hint of sadness.
Phrases:
* Wearing a straight face: This suggests a neutral, impassive expression.
* Looking serious: This is a general description of a stern expression.
* With a furrowed brow: This emphasizes the wrinkles on the forehead that are common with a stern expression.
* With a tight mouth: This highlights the compressed lips that often accompany a stern expression.
The best word or phrase to use will depend on the specific context and the nuances of the expression you want to describe.