What does anaerobic mean?
Anaerobic describes anything that lives, occurs, or functions without free oxygen. In biology and medicine, it characterizes organisms such as certain bacteria, and processes such as fermentation and anaerobic respiration, which generate energy in oxygen's absence; in environmental science, anaerobic digestion is widely used to break down organic waste and produce biogas. In fitness, the word takes on a second meaning: anaerobic exercise refers to short, intense efforts like sprinting or heavy lifting, in which muscles draw on internal energy reserves faster than oxygen can be supplied. The term contrasts directly with aerobic, which denotes processes or activities dependent on oxygen. Coined in the 1860s by Louis Pasteur following his studies of fermentation, anaerobic is now standard across scientific literature and everyday health discourse alike. It carries no emotional connotation, but its precise technical sense makes it indispensable wherever oxygen's presence or absence matters — from wastewater plants to weight rooms to the deep-sea sediments where anaerobic microbes flourish unseen.
Living, occurring, or functioning in the absence of free oxygen; not depending on oxygen for energy production.
"Anaerobic bacteria in the compost pile break down material slowly and produce a distinctive sour smell."
Most frequently encountered in scientific and technical writing, particularly microbiology, medicine, waste management, and exercise science.
Relating to or denoting intense physical exercise of short duration during which the body's demand for oxygen exceeds supply, forcing muscles to generate energy anaerobically.
"Interval sprints are a classic form of anaerobic training that builds explosive power."
This fitness-oriented sense emerged in twentieth-century sports science and is now common in popular health media.
The word 'anaerobic' was coined in the 1860s by Louis Pasteur, who discovered that some microbes don't just tolerate the absence of oxygen — they're actually poisoned by it.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of anaerobic
Anaerobic was coined in French as anaérobie by Louis Pasteur in the early 1860s, during his landmark investigations into fermentation, to describe microorganisms that live without air or oxygen. It combines the Greek-derived prefix an- ('without') with aēr ('air') and bios ('life'), so the literal sense is 'life without air'. English adopted the adjective shortly afterward, alongside the related nouns anaerobe and anaerobiosis, and it spread rapidly through microbiology and physiology. Its sibling terms aerobic and aerobe share the same root components but denote the opposite condition — life and activity dependent on oxygen.
Related word forms
How anaerobic is actually used
A technical term common in biology, medicine, environmental science (waste treatment), and fitness contexts; rarely used in casual conversation except via the familiar phrase 'anaerobic exercise'. Neutral in connotation — neither positive nor negative — though in fitness culture 'anaerobic' often implies intensity and short bursts of effort, while 'aerobic' implies endurance.
Easily confused with anaerobic
Aerobic processes or organisms require oxygen, whereas anaerobic ones occur or live without it.
Anaerobe is a noun referring to an organism that lives without oxygen; anaerobic is the adjective describing such conditions or processes.