/ mjuːl; NAmE / noun
1.
an animal that has a horse and a donkey as parents, used especially for carrying loads :
He's as stubborn as a mule .
2.
( slang ) a person who is paid to take drugs illegally from one country to another
3.
a slipper (= a soft shoe for wearing indoors) that is open around the heel
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WORD ORIGIN
senses 1 to 2 Old English mūl , probably of Germanic origin, from Latin mulus , mula ; reinforced in Middle English by Old French mule .
sense 3 mid 16th cent.: from French , slipper .