1. the quality or state of being contagious; the ability to spread from one person to another through contact or proximity
Usage: typically used in medical or epidemiological contexts
2. the quality of spreading rapidly or influencing others, as with ideas, emotions, or behaviors
Usage: figurative use

Examples

• The contagiousness of the flu virus made it spread quickly through the school.
• Health officials warned about the high contagiousness of the new variant.
• The contagiousness of her enthusiasm inspired the entire team.
• Despite the disease's contagiousness, proper hygiene can reduce transmission.
• The contagiousness of social media trends shows how quickly ideas can spread.
• Scientists studied the contagiousness of the pathogen in laboratory conditions.