What does simultaneity mean?
Simultaneity is the condition of two or more events, actions, or states occurring at the same time. The word is especially useful when the exact coincidence is important, as in discussions of physics, history, psychology, and everyday observation. It can describe an objectively shared moment, such as two clocks striking noon together, or a striking apparent coincidence, such as simultaneous actions performed by different people without prior coordination. In scientific contexts, simultaneity can also mean the absence of a causal or temporal relationship between observed events. Although “simultaneity” is more formal than the simpler phrase “at the same time,” it gives technical or analytical writing a precise focus on timing. Its related adjective, “simultaneous,” describes the events themselves, while “simultaneously” describes how they happen.
nounThe state or condition of happening, occurring, or existing at the same time. It also refers to the fact that two or more events or phenomena are simultaneous.
- The state or condition of two or more things happening, occurring, or existing at the same time.
- The fact or condition that events or phenomena coincide in time, especially when the coincidence is noteworthy or appears unexpected.
"The researchers were struck by the apparent simultaneity of the two seismic events."
"The recording captured the simultaneity of the applause and the final note."
"Economists examined the simultaneity of rising costs and stagnant wages."
The plural is rare and is used mainly when referring to multiple instances of exact or noteworthy temporal coincidence.
"The study considered the simultaneities of several unrelated historical events."
Simultaneity comes from the Latin simul, meaning “at the same time”—the idea that powers clocks, conjuring tricks, and awkward theories about time travel.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does simultaneity come from?
Simultaneity was formed in the early 19th century from the Latin “simultaneus,” meaning “at the same time.” That adjective developed from “simul,” an adverb meaning “together” or “at once,” and ultimately from the same Latin root underlying forms such as “simulate” and “simulacrum.” The noun entered English as a specialist term associated with philosophical and scientific discussions of time and causality.
Related word forms
How simultaneity is actually used
The noun is formal and relatively uncommon in everyday speech. In the humanities and sciences, it can denote an exact coincidence in time or, in physics, the independent occurrence of events without a causal connection.
Easily confused with simultaneity
Simultaneity is the noun naming the state of occurring at the same time, whereas simultaneous is the adjective describing things that occur at the same time.