Past tense of 'chairman' used as a verb; to serve as or act in the role of chairman.
From 'chairman' (a man who presides) with '-ed' as the past tense suffix. This verb form uses 'chairman' as a verb, a practice that has become less common as 'chair' is preferred as a gender-neutral verb.
Using 'chairmen' or 'chairmaned' as verbs feels oddly clunky compared to the simple modern usage of 'to chair' a meeting—it's a great example of how English naturally simplifies longer words over time.
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