What does alveoli mean?
Alveoli are the plural of alveolus, and they refer above all to the millions of microscopic air sacs clustered at the ends of the bronchioles deep within the lungs. It is here that respiration actually happens: oxygen passes through the thin walls of the alveoli into the surrounding capillaries, while carbon dioxide moves the other way to be exhaled. The word also has a dental sense, describing the bony sockets of the jaw that anchor each tooth. Alveoli is a technical term belonging chiefly to medicine, physiology, and dentistry, so it appears most often in clinical, academic, and science-journalism contexts rather than everyday conversation. Its connotations are neutral and precise, though in discussions of diseases such as emphysema, pneumonia, or COVID-19 it can carry serious weight. Understanding alveoli means understanding where breathing does its real work — making the word essential reading for anyone curious about how the body sustains life.
nounThe plural of alveolus; in anatomy, the tiny air sacs at the ends of the bronchioles in the lungs where gas exchange between air and blood takes place. The term is also used in dentistry for the bony sockets in the jaw that anchor the teeth.
- The microscopic air sacs in the lungs where oxygen and carbon dioxide are exchanged with the blood.
- The bony sockets in the upper or lower jaw that hold the roots of the teeth.
"Damage to the alveoli from smoking gradually reduces the lungs' ability to absorb oxygen."
"In emphysema, the walls between adjacent alveoli break down, leaving fewer, larger sacs and less surface area for gas exchange."
"After an extraction, the empty socket left behind in the bone is known as the dental alveolus — the alveoli collectively forming the tooth-bearing ridges of the jaw."
Alveoli is itself the standard plural of the singular noun alveolus, following the Latin pattern. It should not be used as a singular form.
"Healthy lungs contain hundreds of millions of alveoli."
Your lungs contain roughly 480 million alveoli — if you flattened them all out, they would cover a tennis court.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of alveoli
Alveoli comes from Latin alveolus, a diminutive of alveus, meaning a hollow vessel, trough, or belly — literally a 'little hollow'. The anatomical term was adopted into English medical vocabulary in the early modern period, when Latin remained the language of scientific description, and it was applied both to the pulmonary air sacs and to the tooth sockets of the jaw. The same root gives us the adjective alveolar, used in phrases such as 'alveolar ridge' and 'alveolar process'.
Related word forms
How alveoli is actually used
Strictly a plural noun; it is almost never used as a singular. In medical writing 'alveoli' nearly always refers to the pulmonary air sacs unless the context is explicitly dental. Because English speakers often treat Latin plurals awkwardly, some lay sources mistakenly use 'alveoli' for a single sac; careful writers reserve that meaning for 'alveolus'.
Easily confused with alveoli
Alveolus is the singular form referring to one air sac or socket, while alveoli refers to the collection of them.