mule (Noun) — Hybrid offspring of a male donkey and a female horse; usually sterile.
mule (Noun) — A slipper that has no fitting around the heel.
mule (Noun) — A test vehicle fitted with prototype components.
mule (Noun) — A small vehicle or locomotive.
mule (Noun) — (informal) a person paid to smuggle drugs.
mule (Noun) — A stubborn person.