The Collaborative International Dictionary of English v.0.48:

Gules \Gules\ (g[=u]lz), n. [OE. goules, F. gueules, the same
   word as gueule throat, OF. gole, goule, L. gula. So named
   from the red color of the throat. See Gullet, and cf.
   Gula.] (Her.)
   The tincture red, indicated in seals and engraved figures of
   escutcheons by parallel vertical lines. Hence, used
   poetically for a red color or that which is red.
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         His sev'n-fold targe a field of gules did stain
         In which two swords he bore; his word,
         "Divide and reign."                      --P. Fletcher.
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         Follow thy drum;
         With man's blood paint the ground; gules, gules.
                                                  --Shak.
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         Let's march to rest and set in gules, like suns.
                                                  --Beau. & Fl.
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