The Collaborative International Dictionary of English v.0.48:

Sphinx \Sphinx\, n. [L., from Gr. sfi`gx, usually derived from
   sfi`ggein to bind tight or together, as if the Throttler.]
   1.
      (a) In Egyptian art, an image of granite or porphyry,
          having a human head, or the head of a ram or of a
          hawk, upon the wingless body of a lion.
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                The awful ruins of the days of old . . .
                Or jasper tomb, or mutilated sphinx. --Shelley.
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      (b) On Greek art and mythology, a she-monster, usually
          represented as having the winged body of a lion, and
          the face and breast of a young woman.

   Note: The most famous Grecian sphinx, that of Thebes in
         B[oe]otia, is said to have proposed a riddle to the
         Thebans, and killed those who were unable to guess it.
         The enigma was solved by [OE]dipus, whereupon the
         sphinx slew herself. "Subtle as sphinx." --Shak.
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   2. Hence: A person of enigmatical character and purposes,
      especially in politics and diplomacy.
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   3. (Zool.) Any one of numerous species of large moths of the
      family Sphingidae; -- called also hawk moth. See also
      tomato worm.
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   Note: The larva is a stout naked caterpillar which, when at
         rest, often assumes a position suggesting the Egyptian
         sphinx, whence the name.
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   4. (Zool.) The Guinea, or sphinx, baboon (Cynocephalus
      sphinx).
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   Sphinx baboon (Zool.), a large West African baboon
      (Cynocephalus sphinx), often kept in menageries.

   Sphinx moth. (Zool.) Same as Sphinx, 3.
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WordNet (r) 3.0 (2006):

sphinx moth
    n 1: any of various moths with long narrow forewings capable of
         powerful flight and hovering over flowers to feed [syn:
         hawkmoth, hawk moth, sphingid, sphinx moth,
         hummingbird moth]