1. in a way that spreads easily from one person to another
Usage: used to describe diseases or conditions that can be transmitted
2. in a way that influences others through enthusiasm or emotion
Usage: used figuratively to describe spreading emotions or behaviors

Examples

• The virus spread infectiously through the crowded school.
• She laughed infectiously, causing everyone around her to smile.
• His enthusiasm for the project spread infectiously among his teammates.
• The disease was spreading infectiously in the densely populated area.
• Her positive attitude was infectiously uplifting to the entire office.
• The children’s excitement was infectiously joyful during the holiday party.