'apophlegmatic' originates from Late Latin, specifically the word 'apophlegmaticus', from Greek 'apophlegmatikos', where 'apo-' meant 'away' and 'phlegma' meant 'inflammation, phlegm'.

'apophlegmatic' changed from the Medieval/Latin word 'apophlegmaticus' (used in medical Latin) and eventually became the modern English adjective 'apophlegmatic'.

Initially, it meant 'serving to remove phlegm' in a medical/humoral sense, but over time it also took on a rare figurative sense of 'calm, not easily excited'.