The Collaborative International Dictionary of English v.0.48:
Conspiracy \Con*spir"a*cy\, n.; pl. Conspiracies. [See
1. A combination of people for an evil purpose; an agreement,
between two or more persons, to commit a crime in concert,
as treason; a plot.
When shapen was all his conspiracy
From point to point. --Chaucer.
They made a conspiracy against [Amaziah]. --2 Kings
I had forgot that foul conspiracy
Of the beast Caliban and his confederates. --Shak.
2. A concurence or general tendency, as of circumstances, to
one event, as if by agreement.
A conspiracy in all heavenly and earthly things.
3. (Law) An agreement, manifesting itself in words or deeds,
by which two or more persons confederate to do an unlawful
act, or to use unlawful to do an act which is lawful;
Syn: Combination; plot; cabal.