A person who lives in or frequents cloistered spaces, or someone who prefers enclosed environments.
From Latin claustrum (enclosed space, cloister) + -er (agent noun suffix). The Latin root relates to claudere (to close), which also gave us claustrophobia.
This word is rare today, but it reveals how medieval monks and nuns literally shaped the vocabulary we use—they were the original 'clusterers,' retreating into the physical and linguistic worlds they created.
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