maser vs gas maser

maser and gas maser both are nouns.

Word	Noun	Adjective	Verb	Adverb
maser	Yes	No	No	No
gas maser	Yes	No	No	No

As nouns, gas maser is a hyponym of maser; that is, gas maser is a word with a more specific, narrower meaning than maser:

maser: an acronym for microwave amplification by stimulated emission of radiation; an amplifier that works on the same principle as a laser and emits coherent microwave radiation
gas maser: a maser in which microwave radiation interacts with gas molecules

maser (noun)	gas maser (noun)
an acronym for microwave amplification by stimulated emission of radiation; an amplifier that works on the same principle as a laser and emits coherent microwave radiation	a maser in which microwave radiation interacts with gas molecules