The Collaborative International Dictionary of English v.0.48:

Hyena \Hy*e"na\, n.; pl. Hyenas. [L. hyaena, Gr. ?, orig., a
   sow, but usually, a Libyan wild beast, prob., the hyena, fr.
   ? hog: cf. F. hy[`e]ne. See Sow female hog.] (Zool.)
   Any carnivorous mammal of the family Hy[ae]nid[ae], doglike
   nocturnal mammals of Africa and southern Asia, of which three
   living species are known. They are large and strong, but
   cowardly. They feed chiefly on carrion, and are nocturnal in
   their habits. [Written also hy[ae]na.]

   Syn: hyaena.
        [1913 Webster]

   Note: The striped hyena (Hy[ae]na striata) inhabits
         Southern Asia and a large part of Africa. The brown
         hyena (Hy[ae]na brunnea), and the spotted hyena
         (Crocuta maculata), are found in Southern Africa. The
         extinct cave hyena (Hy[ae]na spel[ae]a) inhabited
         England and France.
         [1913 Webster]

   Cave hyena. See under Cave.

   Hyena dog (Zool.), a South African canine animal (Lycaon
      venaticus), which hunts in packs, chiefly at night. It is
      smaller than the common wolf, with very large, erect ears,
      and a bushy tail. Its color is reddish or yellowish brown,
      blotched with black and white. Called also hunting dog.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hyena
    n 1: doglike nocturnal mammal of Africa and southern Asia that
         feeds chiefly on carrion [syn: hyena, hyaena]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "hyena":
   African hunting dog, Cape hunting dog, animal, anthropophagite,
   barbarian, beast, brush wolf, brute, cannibal, coyote, cur,
   destroyer, dingo, dog, fox, hound, insect, jackal, lobo, man-eater,
   medicine wolf, mongrel, nihilist, pig, polecat, prairie wolf,
   reptile, reynard, savage, serpent, shark, skunk, snake, swine,
   tiger, timber wolf, vandal, varmint, vermin, viper, whelp,
   wild man, wolf, worm, wrecker



The Devil's Dictionary (1881-1906):

HYENA, n.  A beast held in reverence by some oriental nations from its
habit of frequenting at night the burial-places of the dead.  But the
medical student does that.