Source : Webster's Revised Unabridged Dictionary (1913)

Spinel \Spi*nel"\, Spinelle \Spi*nelle"\, n. [F. spinelle, or
   LL. spinellus, perhaps from L. spina a thorn, a prickle, in
   allusion to its pointed crystals.] (Min.)
   A mineral occuring in octahedrons of great hardness and
   various colors, as red, green, blue, brown, and black, the
   red variety being the gem spinel ruby. It consist essentially
   of alumina and magnesia, but commonly contains iron and
   sometimes also chromium.

   Note: The spinel group includes spinel proper, also
         magnetite, chromite, franklinite, gahnite, etc., all of
         which may be regarded as composed of a sesquioxide and
         a protoxide in equal proportions.

Spinel \Spin"el\, n.
   Bleached yarn in making the linen tape called inkle;
   unwrought inkle. --Knight.

Source : WordNet®

spinel
     n : a hard glassy mineral consisting of an oxide of magnesium
         and aluminum; occurs in various colors that are used as
         gemstones