A person who countenances or supports something; one who gives approval, encouragement, or tacit permission to an action.
From 'countenance' plus the agent suffix '-er' (one who does something), creating a noun for someone who actively supports or permits something.
This is a rare word because modern English prefers 'supporter' or 'approver'—but 'countenancer' has a subtle implication: someone who merely allows something by not opposing it, rather than actively championing it!
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