The quality or state of being contagious; how readily a disease or influence spreads to others.
From 'contagious' plus the abstract noun suffix '-ness'. This alternative to 'contagiosity' uses the Germanic suffix pattern typical of English rather than the Latinate suffix.
English gives us two ways to say the same thing: 'contagiousness' (from Germanic roots) and 'contagiosity' (from Latin roots)—this duplication shows how English mixed Germanic and Romance language patterns after the Norman Conquest.
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