A person who takes action or initiates legal proceedings; one who acts or brings a lawsuit.
From action (from Latin actio, 'a doing') + -er (agent suffix). Evolved from Middle English actour to denote one who performs actions or brings legal action.
In Scots law, 'actioner' is the standard term for what English law calls a 'plaintiff'—a fascinating linguistic split that shows how legal terminology diverged between Scotland and England after the 1707 Union.
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