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.
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