A cavity or hollow space, especially in zoological or anatomical contexts; a body chamber.
From Latin and Greek koilos 'hollow' combined with the Latin noun suffix -arium 'place of' or 'container for,' following medieval and scientific Latin naming conventions.
Medieval and Renaissance scholars loved creating storage-place nouns with -arium—the same way we have aquarium (water-place) and vivarium (life-place), coelarium literally means the 'hollow-place' inside an organism.
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