The Collaborative International Dictionary of English v.0.48:
Donkey \Don"key\ (d[o^][ng]"k[y^]), n.; pl. Donkeys
(d[o^][ng]"k[i^]z). [Prob. dun, in allusion to the color of
the animal + a dim. termination.]
1. An ass; or (less frequently) a mule.
2. A stupid or obstinate fellow; an ass.
Donkey engine, a small auxiliary engine not used for
propelling, but for pumping water into the boilers,
raising heavy weights, and like purposes.
Donkey pump, a steam pump for feeding boilers,
extinguishing fire, etc.; -- usually an auxiliary.
Donkey's eye (Bot.), the large round seed of the Mucuna
pruriens, a tropical leguminous plant.