Tzetzes' explanation is found nowhere before him. He parses the word as a compound, the second part of which is δῖος "heavenly, divine", and the first member κάρα. Κάρα in Homer means "head", but here Tzetzes understands it as an equivalent of κῆρ "heart", both in the gloss provided for κάρηνον (κάρα/κῆρ ἄνω) and in the gloss provided for καρδία (κάρα is "translated" by κῆρ καὶ ψυχή). That etymology is made possible by the fact that κάρα, Hom. κάρη, which is neuter in Homer, was inflected as a feminine in later poets (κάρην, κάρης): that allows Tzetzes to make the agreement of the adjective δῖα in the feminine, which is the condition for the etymology.