Sphenoid meaning : The sphenoid bone. A wedge-shaped crystal bounded by four equal isosceles triangles; the hemihedral form of a square pyramid. Having a wedged shape. Relating to the compound bone which forms the base of the cranium, behind the eye and below the front part of the brain. It has two pairs of broad lateral ‘wings’ and a number of other projections, and contains two air-filled sinuses.