A person who expresses sympathy or sorrow; someone who condoles or offers condolences.
From 'condole' plus the agent suffix '-er,' which creates nouns meaning 'one who does X.' This follows the standard English pattern of turning verbs into agent nouns (e.g., teacher, player, runner).
This word barely exists in modern usage—we'd say 'someone expressing condolences' instead of 'a condoler,' showing how some agent nouns are just too awkward to survive in real language, despite being grammatically perfect.
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