'Contagion' is Latin for 'touching together' — the Romans knew disease spreads through contact.
The communication of disease from one person or organism to another by close contact; a disease spread by close contact; the spreading of a harmful idea or practice.
From Latin contāgiō (a touching, contact, contagion), accusative contāgiōnem, from contingere (to touch closely), composed of con- (together) + tangere (to touch). The PIE root is *teh₂g- (to touch, to handle), which also underlies Latin taxāre (to touch sharply, to assess), English tact, tangent, and intact. The word captures the Roman empirical observation that disease spreads through physical touching — a person contaminated
Before germ theory, 'contagion' was one of three competing models for how disease spread. 'Contagion' (disease passes by touch), 'miasma' (disease comes from bad air), and 'divine punishment' (disease comes from sin) were all taken seriously by physicians. The etymological insight embedded in 'contagion' — that disease spreads by contact — turned out to be closer to the truth than its rivals, vindicating the word's Latin creators two millennia later.
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