auxiliary boiler vs donkey boiler

auxiliary boiler and donkey boiler both are nouns.

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

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

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

auxiliary boiler (noun)	donkey 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)