Example:
The army mule, used to transport equipment up in the mountains, had neither the elegance of its father, a horse, nor the good nature of its mother, a donkey. 
greg westfall
Photo license:
CC: Attribution, Commercial Use
Regionalism:
Neutral
Regional variant:
Neutral
Full Expression:
The “ool” Sound ( /u:/ ) : mule
an animal resulting from a horse crossed with a donkey