phlegmatic
definition
(of a person) having an unemotional and stolidly calm disposition
example
The phlegmatic British character
synonyms
self-controlledcalmcoolapathetic
word origin — Middle English (in the sense ‘relating to the humor phlegm’): from Old French fleumatique, via Latin from Greek phlegmatikos, from phlegma ‘inflammation’ (see phlegm)