mule1
  
  n.
     - the offspring of a male donkey and a female horse, typically sterile. Compare with hinny1.
- a hybrid plant or animal, especially a sterile one.
- an obstinate person.
- informal a courier for illegal drugs.
- 
(also spinning mule)
 a kind of spinning machine producing yarn on spindles.
Etymology
  OE mūl, prob. of Gmc origin, from L. mulus, mula.
 
  
    
mule2
  
  n.
 a slipper or light shoe without a back.
Etymology
  C16: from Fr., ‘slipper’.