Compositional etymology. It is not immediately clear in Orion because the text is altered. The original etymology was μεγάλα κεύθειν. But Orion, or a later a copyist, replaced καύθειν by its synonym χωρεῖν "to contain", thereby preserving the semantic justification of the etymology but losing the formal one. This results in an elliptic etymology. The mistake is repeated in the Etym. Magnum. Orion's text as printed by Sturz has μεγάλας χωρεῖν. The Etym. Magnum has μεγάλως, which is certainly the correct reading, and μεγάλας is a mistake.