Stronger synonyms:
* Horrified: Emphasizes intense fear and disgust.
* Appalled: Suggests shock and disapproval.
* Terrified: Focuses on intense fear.
* Dismayed: Implies disappointment and a feeling of being defeated.
* Stunned: Indicates being completely shocked and unable to react.
Milder synonyms:
* Astonished: Emphasizes surprise and amazement.
* Surprised: Indicates a feeling of being caught off guard.
* Alarmed: Suggests a sense of danger or threat.
* Shocked: A general word for a sudden, strong reaction.
The best synonym for "aghast" will depend on the specific context of your writing.