skiagraph vs X ray

skiagraph and X ray both are nouns.

Word	Noun	Adjective	Verb	Adverb
skiagraph	Yes	No	No	No
X ray	Yes	No	No	No

As nouns, X ray is a hyponym of skiagraph; that is, X ray is a word with a more specific, narrower meaning than skiagraph:

skiagraph: a photographic image produced on a radiosensitive surface by radiation other than visible light (especially by X-rays or gamma rays)
X ray: a radiogram made by exposing photographic film to X rays; used in medical diagnosis

Other hyponyms of skiagraph include autoradiograph, roentgenogram, X-ray, X-ray photograph, X-ray picture.

skiagraph (noun)	X ray (noun)
a photographic image produced on a radiosensitive surface by radiation other than visible light (especially by X-rays or gamma rays)	a radiogram made by exposing photographic film to X rays; used in medical diagnosis
	electromagnetic radiation of short wavelength produced when high-speed electrons strike a solid target