phlegmatic
Staying calm and not getting easily excited or upset.
Someone who is phlegmatic stays calm and unbothered even when things get chaotic or exciting around them. While others might panic during a fire drill or get overexcited about a field trip, a phlegmatic person remains steady and composed.
The word describes a temperament that's hard to rattle. A phlegmatic friend might respond to surprising news with a simple “huh, interesting” while everyone else gasps and talks over each other. A phlegmatic teacher stays patient when the classroom gets noisy. A phlegmatic goalkeeper doesn't flinch when the opposing team charges toward the goal.
This calmness can be a strength: phlegmatic people often think clearly in emergencies and don't get swept up in drama. But it can also mean they seem unenthusiastic or hard to excite. While others are cheering about winning a game, a phlegmatic teammate might just nod and say “good job.”
Similar words include stolid and impassive, though phlegmatic specifically suggests a calm, unhurried quality rather than coldness or lack of feeling.