combat ceiling vs service ceiling

combat ceiling and service ceiling both are nouns.

Word	Noun	Adjective	Verb	Adverb
combat ceiling	Yes	No	No	No
service ceiling	Yes	No	No	No

As nouns, combat ceiling and service ceiling are synonyms defined as:

combat ceiling and service ceiling: altitude above which a plane cannot climb faster than a given rate

combat ceiling (noun)	service ceiling (noun)
altitude above which a plane cannot climb faster than a given rate	altitude above which a plane cannot climb faster than a given rate