A person or thing that splashes, sprays, or spatters something onto other things.
From 'bespatter' plus the '-er' agent suffix, which creates nouns for things or people that perform an action. This follows the productive English pattern of adding '-er' to verbs to name the agent.
We don't use 'bespatterer' much today, but older texts—especially British Victorian writing—loved these '-er' agent nouns for specific people, showing how language naturally creates new nouns when there's a need to name specific roles or professions.
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