phlegm

The Greek 'phlegma' (φλέγμα) comes from 'phlegein' (φλέγειν), meaning to burn or to flame. In Hippocratic medicine of the 5th century BCE, 'phlegma' first named inflammation and the heat of fever, not the cold, sluggish substance we know. The four-humor system of Galen, writing in the 2nd century CE, gave phlegm its current character: the cold, moist humor associated with water, winter, and a particular temperament.

Latin borrowed the Greek 'phlegma' directly, and the word passed through medieval medical Latin with no change in spelling. Old French took it as 'fleume' or 'flegme' around 1200, and Middle English received both forms. The spelling 'phlegm' reflects a 16th-century Latinization, a learned correction that restored the Greek 'ph' and the silent 'g' from 'phlegma.' This is why English spells the word the way a Renaissance scholar imagined Greeks wrote.

Galen's theory held that the body was governed by blood, yellow bile, black bile, and phlegm. Each humor had a season, an element, an organ, and a corresponding temperament. Too much phlegm produced the phlegmatic person: slow, calm, unemotional, resistant to change. Robert Burton's 'The Anatomy of Melancholy' (1621) analyzed all four humors at exhaustive length, and phlegm appears hundreds of times.

The medical theory died, but the word survived, carrying the character of the humor into the adjective 'phlegmatic.' The physical substance, the mucus of the throat and lungs, kept its name through the centuries. Samuel Johnson's 1755 dictionary defined phlegm as 'the watery humour' and noted the phlegmatic temperament. Today a doctor uses the word in a purely physiological sense while a novelist uses 'phlegmatic' to describe a character who never loses composure.