A person or animal that caterwauls; someone who makes loud, unpleasant wailing sounds.
From 'caterwaul' (the verb) plus the agent suffix '-er' (one who does the action). This follows standard English word formation where '-er' is added to verbs to name the person performing that action.
This is a delightfully specific insult from medieval times—instead of just saying someone was loud and annoying, you could call them a 'caterwauler' and everyone would picture a screeching cat, which made the insult much more vivid and funny!
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