Imperturbable is an adjective that means unable to be upset or excited.

The Latin word pertubare (per too BAR ay) means to disturb, and it was later  the origin of ‘perturb.’  Our word of the day may refer to someone who cannot be disturbed or upset. For example, Eric had such an imperturbable demeanor that even the sight of his favorite team losing in overtime didn’t seem to bother him. I, on the other hand, was deeply traumatized by the game’s result.