The Collaborative International Dictionary of English v.0.48:

Jenny \Jen"ny\, n.; pl. Jennies.
   [1913 Webster]
   1. A familiar or pet form of the proper name Jane.
      [1913 Webster]

   2. (Zool.) A familiar name of the European wren.
      [1913 Webster]

   Jenny ass (Zool.), a female ass; also, a female of certain
      other animals.
      [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Jenny \Jen"ny\, n. [A corruption of gin an engine; influenced by
   Jenny, the proper name. See Gin an engine, and cf.
   Ginny-carriage.]
   A machine for spinning a number of threads at once, -- used
   in factories. Also called spinning jenny.
   [1913 Webster]

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):

Jenny
    n 1: United States architect who designed the first skyscraper
         in which a metal skeleton was used (1832-1907) [syn:
         Jenny, William Le Baron Jenny]
    2: female donkey [syn: jennet, jenny, jenny ass]

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "jenny":
   Partlet, Rocky Mountain canary, ass, biddy, bitch, bossy,
   brood mare, burro, cow, cuddy, dickey, doe, donkey, ewe, ewe lamb,
   filly, guinea hen, gyp, heifer, hen, hind, jack, jackass, jennet,
   jenny ass, lioness, mare, mule, nanny, nanny goat, neddy, peahen,
   roe, she-bear, she-goat, she-lion, silkworm, slut, sow, spider,
   spinner, spinning frame, spinning jenny, spinster, throstle,
   tigress, vixen