A person who takes part in forming or carrying out a conspiracy or secret harmful plan.
From 'complot' plus the agent suffix '-er', meaning 'one who complots.' The word appears in 16th-century political literature describing those involved in conspiracies.
A 'complotter' was a dangerous person to be labeled as in Renaissance Europe—the word carried weight because actual plottings could result in execution, so accusing someone of being a complotter was a serious political charge.
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