orbitosphenoid Syllabification: (or·bi·to·sphe·noid)Pronunciation: /ˌôrbitōˈsfēˌnoid/ (also orbitosphenoid bone)Definition of orbitosphenoid noun Anatomy & Zoology a bone in the floor of the mammalian cranium, in the region of the optic nerve. In the human skull it is represented by the lesser wings of the sphenoid bone. orbitosphenoid in other Oxford dictionaries Definition of orbitosphenoid in the British & World English dictionary