stoic
Meaning: unaffected by passion or feeling
Usage: The stoic student accepted the disappointing grade without complaint.
impassive
Meaning: showing no emotion; expressionless
Usage: Stop being so impassive; it’s healthy to cry every now and then.
equanimity
Meaning: composure
Usage: Even though he had just been fired, Mr. Simms showed great equanimity by neatly packing up his desk and wishing everyone in the office well.
nonchalant
Meaning: having a lack of concern, indifference
Usage: Although deep down she was very angry, Marsha acted in a nonchalant manner when she found out that her best friend had used her clothing without asking.
stolid
Meaning: expressing little sensibility, unemotional
Usage: The stolid goalie showed no reaction after the missed shot.