sky marshal vs air marshal

sky marshal and air marshal both are nouns.

Word	Noun	Adjective	Verb	Adverb
sky marshal	Yes	No	No	No
air marshal	Yes	No	No	No

As nouns, sky marshal and air marshal are synonyms defined as:

sky marshal and air marshal: a person trained by the government in hijacking and terrorist tactics who (for security reasons) is a passenger aboard an airline flight

sky marshal (noun)	air marshal (noun)
a person trained by the government in hijacking and terrorist tactics who (for security reasons) is a passenger aboard an airline flight	a person trained by the government in hijacking and terrorist tactics who (for security reasons) is a passenger aboard an airline flight