What does equiprobable mean?
"Equiprobable" is a technical adjective meaning equally probable — used when two or more possible outcomes have exactly the same chance of occurring. It appears most often in mathematics, statistics, and the physical sciences, where precision matters: in a fair die roll, for instance, all six faces are equiprobable, and in statistical mechanics certain physical states are treated as equiprobable when calculating probabilities. The word is built from the Latin prefix "equi-," meaning equal, joined to "probable," and it carries a formal, analytical tone that can feel stiff in everyday speech, where speakers typically prefer "equally likely." Its noun form, "equiprobability," names the property itself. Though rarely heard outside academic and scientific contexts, "equiprobable" fills a genuine gap in English by compressing the phrase "having equal probability" into a single precise term.
adjectiveHaving an equal or the same probability of occurring; equally likely.
- (Of two or more possible outcomes) Having equal probability; equally likely to occur.
"In an ideal die roll, all six outcomes are equiprobable."
"The theory assumes that every microstate of the system is equiprobable."
"Because the cards were well shuffled, each of the four players considered every remaining card equally probable."
Flip a fair coin and you've witnessed equiprobability in action — two outcomes locked in perfect mathematical dead heat.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of equiprobable
"Equiprobable" combines the Latin-derived prefix "equi-," from "aequus" meaning equal, with "probable," from the Latin "probabilis," meaning provable or credible. It emerged as a technical coinage alongside the rise of modern probability theory, rather than descending through centuries of literary use. Its cognates include other "equi-" formations such as "equidistant" and "equivalent," as well as the broader family of "probable" words like "probability" and "improbable."
Related word forms
How equiprobable is actually used
Primarily a technical term found in mathematics, statistics, physics, and formal writing; it sounds stilted in casual conversation, where "equally likely" is preferred.
Easily confused with equiprobable
"Probable" means merely likely to happen, whereas "equiprobable" specifically means having exactly the same likelihood as something else.