Related Clues:

• Not easily flapped
• Betraying no emotion
• Giving nothing away, in a way
• Uncomplaining sort
• Follower of the philosopher Epictetus
• Not to be taken lightly
• Having a stiff upper lip
• Not overly emotional
• Not moved much
• Not reacting to pain, say
• Hard to stir
• Epictetus, for one
• Glowering
• Marcus Aurelius was one
• In a sullen mood