multiengine airplane vs multiengine plane

multiengine airplane and multiengine plane both are nouns.

Word	Noun	Adjective	Verb	Adverb
multiengine airplane	Yes	No	No	No
multiengine plane	Yes	No	No	No

As nouns, multiengine airplane and multiengine plane are synonyms defined as:

multiengine airplane and multiengine plane: a plane with two or more engines

multiengine airplane (noun)	multiengine plane (noun)
a plane with two or more engines	a plane with two or more engines