The Collaborative International Dictionary of English v.0.48:

Mule \Mule\ (m[=u]l), n. [F., a she-mule, L. mula, fem. of
   mulus; cf. Gr. my`klos, mychlo`s. Cf. AS. m[=u]l, fr. L.
   mulus. Cf. Mulatto.]
   1. (Zool.) A hybrid animal; specifically, one generated
      between an ass and a mare. Sometimes the term is applied
      to the offspring of a horse and a she-ass, but that hybrid
      is more properly termed a hinny. See Hinny.
      [1913 Webster]

   Note: Mules are much used as draught animals. They are hardy,
         and proverbial for stubbornness.
         [1913 Webster]

   2. (Bot.) A plant or vegetable produced by impregnating the
      pistil of one species with the pollen or fecundating dust
      of another; -- called also hybrid.
      [1913 Webster]

   3. A very stubborn person.
      [1913 Webster]

   4. A machine, used in factories, for spinning cotton, wool,
      etc., into yarn or thread and winding it into cops; --
      called also jenny and mule-jenny.
      [1913 Webster]

   5. A slipper that has no fitting around the heel.

   Syn: mules, scuff, scuffs.
        [WordNet 1.5]

   Mule armadillo (Zool.), a long-eared armadillo (Tatusia
      hybrida), native of Buenos Ayres; -- called also mulita.
      See Illust. under Armadillo.

   Mule deer (Zool.), a large deer (Cervus macrotis syn.
      Cariacus macrotis) of the Western United States. The
      name refers to its long ears.

   Mule pulley (Mach.), an idle pulley for guiding a belt
      which transmits motion between shafts that are not
      parallel.

   Mule twist, cotton yarn in cops, as spun on a mule; -- in
      distinction from yarn spun on a throstle frame.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mule
    n 1: hybrid offspring of a male donkey and a female horse;
         usually sterile
    2: a slipper that has no fitting around the heel [syn: mule,
       scuff]

Moby Thesaurus II by Grady Ward, 1.0:

86 Moby Thesaurus words for "mule":
   Cape Colored, Eurasian, Siberian husky, ass, bastard,
   beast of burden, bigot, bitter-ender, bullethead, camel, cattalo,
   citrange, cross, crossbred, crossbreed, diehard, dogmatist, donkey,
   draft animal, dromedary, elephant, fanatic, griffe, half blood,
   half-bred, half-breed, half-caste, hardnose, high yellow, hinny,
   horse, husky, hybrid, intransigeant, intransigent, jennet, jenny,
   ladino, last-ditcher, liger, llama, malamute, manlike, manly,
   masculine, maverick, mestee, mestiza, mestizo, metis, metisse,
   mixblood, mixed-blood, mongrel, mulatto, mustee, octoroon, ox,
   pack horse, perverse fool, pighead, plumcot, positivist, purist,
   quadroon, quintroon, reindeer, sambo, silkworm, sledge dog, spider,
   spinner, spinning frame, spinning jenny, spinster, standpat,
   standpatter, stickler, sumpter, sumpter horse, sumpter mule,
   tangelo, throstle, tigon, zebrass, zebrule



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

MULE
       MULtilingual Enhancement of GNU EMACS (EMACS, GNU)


The Free On-line Dictionary of Computing (30 December 2018):

Mule

    A multi-lingual enhancement of GNU Emacs.  Mule
   can handle not only ASCII characters (7 bit) and ISO
   Latin 1 characters (8 bit), but also 16-bit characters like
   Japanese, Chinese, and Korean.  Mule can have a mixture of
   languages in a single buffer.

   Mule runs under the X window system, or on a Hangul
   terminal, mterm or exterm.

   (ftp://etlport.etl.go.jp/pub/mule).

   (1996-01-28)


Easton's 1897 Bible Dictionary:

Mule
   (Heb. pered), so called from the quick step of the animal or its
   power of carrying loads. It is not probable that the Hebrews
   bred mules, as this was strictly forbidden in the law (Lev.
   19:19), although their use was not forbidden. We find them in
   common use even by kings and nobles (2 Sam. 18:9; 1 Kings 1:33;
   2 Kings 5:17; Ps. 32:9). They are not mentioned, however, till
   the time of David, for the word rendered "mules" (R.V.
   correctly, "hot springs") in Gen. 36:24 (yemim) properly denotes
   the warm springs of Callirhoe, on the eastern shore of the Dead
   Sea. In David's reign they became very common (2 Sam. 13:29; 1
   Kings 10:25).

     Mules are not mentioned in the New Testament. Perhaps they had
   by that time ceased to be used in Palestine.