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)
