What does infectious mean?
Infectious is an adjective describing a disease, organism, or other agent capable of causing or transmitting infection. In medical and public-health language, it is especially important because identifying an infectious disease signals the possibility of transmission and may justify measures such as isolation, hygiene, or vaccination. The word can also describe a person whose enthusiasm, laughter, or personality draws others in. This figurative use is strongly positive: an infectious joke makes people laugh, while infectious enthusiasm inspires a group. The term is common in both British and American English and is often paired with words such as disease, highly, and agent. Although contagious overlaps with infectious, infectious more directly concerns the cause or capacity of infection, while contagious often emphasizes the ease of person-to-person spread. Outside medicine, infectious is usually figurative rather than literal and conveys immediacy, appeal, and a quality that spreads through social interaction.
adjectiveCapable of causing infection or being transmitted from one organism to another, especially a disease. It can also describe a person, place, or thing that spreads infection, and figuratively, something that spreads enthusiasm or captures others' attention.
- Capable of causing infection or being transmitted between organisms.
- Belonging to or associated with an infectious disease.
- Spreading easily or rapidly, especially through contact.
- Figuratively, able to spread enthusiasm, amusement, or interest to others.
- Figuratively, so compelling or appealing that it attracts widespread attention.
"The highly infectious disease prompted the school to cancel classes for the week."
"Researchers warned that the new strain was highly infectious and could spread rapidly through the community."
"Her infectious sense of humor made strangers feel immediately welcome."
Infectious is both a medical warning and a social compliment: it can describe a dangerous disease or an irresistible laugh.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does infectious come from?
Infectious comes through French from Latin infectiosus, meaning “contagious” or “liable to infection.” Its ultimate roots lie in the Latin verb inficere, formed from in- “into” and facere “to make,” originally referring to putting something into or contaminating something else. Related English forms include infect, infection, infective, and disinfect. The established English adjective dates from the late Middle English period and retains both its medical sense and its later figurative development.
How infectious is actually used
In medical contexts, infectious is a precise term for a disease or agent capable of causing infection. In everyday figurative use, it is usually positive and suggests an energy or quality that spreads easily to other people. It is not usually used to mean merely visible or obvious.
Easily confused with infectious
Infectious emphasizes the ability of a disease or organism to cause infection, while contagious often emphasizes being easily passed from person to person.
Infectious describes something capable of transmitting infection, whereas infected describes someone or something that has already contracted an infection.