Fair enough. What would you call it *inside* mythology?
The umbrella term for such fused creatures is 'chimera'.
Thanks, but that's referring to two separate creatures who got attached accidentally while developing. I'm talking about a straight cross (one parent dragon, one parent horse).
You might want to check-out Kelpie, Hippocamp, Ceffyl Dŵr, Each uisge, and other related mythical horse creatures on wikipedia. There's no dragon relationship mentioned there but some of the critters have a definite mean streak in them which might be attributable to a dragon progenitor. You may want to suggest the link.