mid-14c., "action of observing or testing; an observation, test, or trial;" also "piece of evidence or empirical proof; feat of magic or sorcery," from Old French esperment "practical knowledge, cunning; enchantment, magic spell; trial, proof, example; lesson, sign, indication," from Latin experimentum "a trial, test, proof, experiment," noun of action from experiri "to try, test," from ex "out of" (see ex-) + peritus "experienced, tested," from PIE *per-yo-, suffixed form of root *per- (3) "to try, risk."

"make trial, operate (on something) so as to discover some unknown fact or to establish it when known," late 15c., from experiment (n.). Intransitive sense by 1787. Related: Experimented; experimenting.

"the act or practice of making experiments, the process of experimenting," 1670s, noun of action from experiment (v.).

Proto-Indo-European root meaning "to try, risk," an extended sense from root *per- (1) "forward," via the notion of "to lead across, press forward."

It forms all or part of: empiric; empirical; experience; experiment; expert; fear; parlous; peril; perilous; pirate.

It is the hypothetical source of/evidence for its existence is provided by: Latin experiri "to try," periculum "trial, risk, danger;" Greek peira "trial, attempt, experience," empeiros "experienced;" Old Irish aire "vigilance;" Old English fær "calamity, sudden danger, peril, sudden attack," German Gefahr "danger," Gothic ferja "watcher.

in reference to the famous 1887 experiment which disproved the existence of scientific "ether," it is from the names of the physicists who conducted it, Albert A. Michelson and Edward W. Morley.

late 14c., "observation as the source of knowledge; actual observation; an event which has affected one," from Old French esperience "experiment, proof, experience" (13c.), from Latin experientia "a trial, proof, experiment; knowledge gained by repeated trials," from experientem (nominative experiens) "experienced, enterprising, active, industrious," present participle of experiri "to try, test," from ex "out of" (see ex-) + peritus "experienced, tested," from PIE *per-yo-, suffixed form of root *per- (3) "to try, risk." Meaning "state of having done something and gotten handy at it" is from late 15c.

"danger, risk, hazard, jeopardy, exposure of person or property to injury, loss, or destruction," c. 1200, from Old French peril "danger, risk" (10c.), from Latin periculum "an attempt, trial, experiment; risk, danger," with instrumentive suffix -culum and first element from PIE *peri-tlo-, suffixed form of root *per- (3) "to try, risk."