The Collaborative International Dictionary of English v.0.48:

Musca \Mus"ca\, prop. n.; pl. Muscae. [L., a fly.]
   1. (Zool.) A genus of dipterous insects, including the common
      house fly, and numerous allied species.
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   Note: Formerly, a large part of the Diptera were included
         under the genus Musca.
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   2. (Astron.) A small constellation situated between the
      Southern Cross and the Pole.
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   Muscae volitantes. [L., flying flies.] (Med.) Specks or
      filaments apparently seen moving or gliding about in the
      field of vision. Their appearance is often a symptom of
      disease of the eye, or of disorder of the nervous system.
      [1913 Webster] Muscadel