A person who chairs or presides over a meeting, committee, or organization.
From English 'chair' (from Old French 'chaire', from Latin 'cathedra') plus the agent suffix '-er' meaning 'one who does.' The meaning evolved from someone sitting in a specific seat of authority to someone who holds that authority.
The word 'chairer' is rarely used today because we prefer 'chairperson' or 'chair' itself—but linguistically, it shows how English adds '-er' to almost any verb to make agent nouns, a pattern so productive that new '-er' words are constantly created.
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