phlegmatism
/ˈflɛɡmətɪz(ə)m/noun
Phlegmatic nature, character, or temperament; calmness, stolidity, absence of excitability.
Origin
Late 17th century; earliest use found in Randle Holme (1627–1700), herald painter. From phlegmat- + -ism. Compare post-classical Latin phlegmatismus (in an undated glossary).