infectious

Etymology

It is formed from English infection + -ous,^[2][3][4] Infection comes from Old French infeccion and Late Latin īnfectiō (“infection, contagion”), from īnficiō (“to spoil, stain”).^[3] Earlier words in the same sense were infectuous (late 15th century) and infective (late 14th century).^[3][2][5]

Earliest recorded meaning

Causing or spreading disease, especially of an epidemic kind: 1534, in T. Paynell's translation of a treatise against the plague.^[2][4] Etymonline dates the word to the 1540s.^[3]

Semantic evolution

Of a disease itself, capable of spreading from one person or animal to another, it is recorded from 1575.^[2] In the 16th century it could also mean infected (1542 to 1727) and venomous (1585 to 1658).^[2] By 1574 it was used of things that taint the character or morals, and in Beaumont and Fletcher (1619) of actions and emotions that spread easily from one person to another, such as laughter.^[2][3] In 19th-century international law, infectious contraband made the rest of a cargo, or the ship, liable to seizure (1812).^[2][6]

Timeline

• 1534 – causing or spreading disease.^[2][4]
• 1542 – infected (until 1727).^[2]
• 1574 – corrupting morals or character.^[2]
• 1575 – of a disease, transmissible.^[2]
• 1619 – of an emotion or action, easily spread.^[2][3]
• 1812 – (international law) of contraband.^[2]
• 1824 – used in the care of infectious patients.^[2]

Modern meaning

Adjective

1. Of a disease, caused by microorganisms such as bacteria or viruses and able to spread from one person or animal to another.
2. Capable of causing infection; likely to pass on a disease.
3. Of a feeling or action, spreading quickly to others: His laugh was so infectious that the whole room joined in.
4. (international law) Of goods, making the rest of a cargo liable to seizure.

Word family

• infectiously
• infectiousness
• uninfectious
• infectious mononucleosis

Related words

• infect
• infection
• infective
• contagious

Usage notes

Etymonline notes that from the 1540s infection meant disease passed on through air or water, as distinct from contagion, passed from body to body.^[3] Chambers keeps a similar distinction, defining a contagious disease as one spread by ordinary social contact, in contrast with infectious.^[7]

References

1. ^ Wiktionary, the free dictionary, https://en.wiktionary.org
2. ^ a b c d e f g h i j k l m n Oxford English Dictionary Online (accessed March 2026), Oxford: Oxford University Press
3. ^ a b c d e f g Harper, Douglas. Online Etymology Dictionary, https://www.etymonline.com
4. ^ a b c Merriam-Webster Unabridged Dictionary (2024), online ed., Springfield, Mass.: Merriam-Webster
5. ^ Shorter Oxford English Dictionary on Historical Principles (2002), 5th ed., ed. William R. Trumble and Angus Stevenson, Oxford: Oxford University Press
6. ^ Collins English Dictionary (2023), Glasgow: HarperCollins
7. ^ The Chambers Dictionary (2008), 11th ed., Edinburgh: Chambers Harrap