donkey boiler vs auxiliary boiler

donkey boiler and auxiliary boiler both are nouns.

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

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

donkey boiler and auxiliary boiler: (nautical) an extra boiler (as a ship's boiler that is used while the ship is in port)

donkey boiler (noun)	auxiliary boiler (noun)
(nautical) an extra boiler (as a ship's boiler that is used while the ship is in port)	(nautical) an extra boiler (as a ship's boiler that is used while the ship is in port)