Gelatinous Cube

gelatinous cube, n., D&D-ism a dungeon-dwelling slime or ooze monster, in the shape of a 10' x 10' cube; so designed to fill and navigate the corridors of the typical D&D dungeon. [GJ1]
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Addendum: The ubiquitous, ridiculous gelatinous cube is one of the dumbest monsters associated with Dungeons & Dragons; woe to the player whose beloved character is consumed by giant roaming Knox Blox. See gelatinous lozenge [EDE]