'Donkey pump' definitions:

Definition of 'donkey pump'

noun

A supplementary pump available if needed [syn: auxiliary pump, donkey pump]

From: GCIDE

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. [1913 Webster]
2. A stupid or obstinate fellow; an ass. [1913 Webster]
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. [1913 Webster]