sphenoid

views updated May 08 2018

sphenoid A wedge-shaped, four-faced, closed form, normally occurring in the tetragonal or orthorhombic crystal systems, but with a special form (the ‘mono-clinic sphenoid’, or ‘dihedron’) occurring in the monoclinic system. The terminology for sphenoidal forms is complex and inconsistent, although in general the crystallographic axes emerge at the centre of the edges where pairs of triangular faces meet.

A Dictionary of Earth Sciences AILSA ALLABY and MICHAEL ALLABY

sphenoid

views updated May 18 2018

sphenoid (anat.) irregularly-shaped bone at the base of the skull wedged in between other bones. XVIII. — Gr. sphēnoeidēs, f. sphēn wedge; see -OID
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The Concise Oxford Dictionary of English Etymology T. F. HOAD