A cellar is a room or space under a building, usually used for storage. It is often cool and dark and may be partly or completely underground.
From Old French 'celier', from Latin 'cellarium' meaning 'storeroom', from 'cella' (small room). It originally referred to a place for storing food and wine.
A cellar is just a 'cell' that got promoted to a storage specialist. The same root that gave us biological 'cells' gave us these underground rooms, all built on the idea of small enclosed spaces.
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