A person who expresses strong disapproval or regret; one who deplores something.
From deplore + -er (Old English suffix forming agent nouns). The -er suffix creates nouns for people who perform an action.
English loves to make nouns for people doing things (-er, -ist, -or, etc.), but 'deplorer' is unusual because it focuses on the emotional act rather than a profession or identity—most -er words describe what someone regularly does, not momentary disapproval.
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