Definition of mule
1 a
:a hybrid between a horse and a donkey;
especially
:the offspring of a male donkey and a mare
b
:a self-sterile plant whether hybrid or not
c
:a usually sterile hybrid
2
:a very stubborn person
3
:a machine for simultaneously drawing and twisting fiber into yarn or thread and winding it into cops
4
slang
:a person who smuggles or delivers illicit substances (such as drugs)
