The building blocks of English

Affixes

sphen(o)-

Wedge-shaped.

Greek sphēn, wedge.

The sphenoid bone (frequently abbreviated to sphenoid) forms the base of the cranium behind the eyes; spheno‑ is used in medicine to refer to this bone together with another part of the skull: sphenopalatine, the sphenoid plus the palate; sphenoethmoid, the sphenoid plus the ethmoid, a square bone at the root of the nose.

Outside medicine, sphenoid is a general adjective to describe something wedge-shaped; the Sphenopsida is a class of plants including the horsetails (Greek opsis, appearance); sphene is a mineral that occurs in wedge-shaped crystals; a sphenogram is a rather rare term for a wedge-shaped cuneiform character.