Mezanne rolled a glob of immortal stuff between her hands. She was bored with all her toys, and wanted new ones. Ones like those hounds Havrek had, but better. Ones that would take the field by storm and rip everything in their path to ribbons. An idea formed in her mind, and she molded the stuff until it was a great, powerful creature. Its shape was like a large dog, but winged, and...scaled, yes, covered with scales. Large fangs and claws, and like all her minions, spikes where it seemed reasonable to have them.
She stood back from her creation, then tweaked it a tiny bit here and there. It was properly fearsome, as all her creatures were, and she decided to name the species 'dragon'.