/ kənˈspɪrəsi; NAmE / noun
[ C , U ] ( pl. -ies ) conspiracy (to do sth) | conspiracy (against sb/sth) a secret plan by a group of people to do sth harmful or illegal :
a conspiracy to overthrow the government
conspiracies against the president
a conspiracy of silence (= an agreement not to talk publicly about sth which should be made public)
They were charged with conspiracy to murder.
a conspiracy theory (= the belief that a secret conspiracy is responsible for a particular event)
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WORD ORIGIN
late Middle English : from Anglo-Norman French conspiracie , alteration of Old French conspiration , based on Latin conspirare agree, plot, from con- together with + spirare breathe.