'antiphlegmatic' originates from New Latin 'antiphlegmaticus', ultimately from Greek 'antiphlegmatikos', where 'anti-' meant 'against' and 'phlegma' meant 'inflammation' or 'phlegm'.

'antiphlegmatic' changed from Late Latin 'antiphlegmaticus' (used in medical Latin) and New Latin formations into English medical usage in the 17th century, becoming the modern English adjective 'antiphlegmatic'.

Initially, it meant 'acting against phlegm or inflammation' in the context of humoral medicine; over time it has retained that medical sense but is now rare and occasionally used figuratively to mean 'not phlegmatic' (not sluggish or stolid).