Origin: Latin suffix -ous
Infectious has 4 different meanings across 1 category:
caused by infection or capable of causing infection
"viruses and other infective agents"
"a carrier remains infective without himself showing signs of the disease"
Transmitted from one person to another, usually through the air breathed.
"The doctor warned that the patient had an infectious cough that could easily spread to others in the waiting room."
In plain English: Infectious means something that can spread from person to person, usually by causing an illness.
"His cheerful laugh was so infectious that everyone in the room started smiling too."
Usage: Use infectious to describe diseases or moods that spread easily between people, such as colds or laughter. Avoid confusing it with contagious when referring specifically to non-physical traits like humor or enthusiasm.
The word infectious comes from the New Latin term īnfectiōnus, which was formed by combining "infect" with the suffix "-ious." It entered English to describe something that has the power to spread or contaminate others.