donkey engine vs auxiliary engine

donkey engine and auxiliary engine both are nouns.

Word	Noun	Adjective	Verb	Adverb
donkey engine	Yes	No	No	No
auxiliary engine	Yes	No	No	No

As nouns, donkey engine and auxiliary engine are synonyms defined as:

donkey engine and auxiliary engine: (nautical) a small engine (as one used on board ships to operate a windlass)

donkey engine (noun)	auxiliary engine (noun)
(nautical) a small engine (as one used on board ships to operate a windlass)	(nautical) a small engine (as one used on board ships to operate a windlass)
a locomotive for switching rolling stock in a railroad yard