viewing vs preview

viewing and preview both are nouns.

Word	Noun	Adjective	Verb	Adverb
viewing	Yes	No	No	No
preview	Yes	No	Yes	No

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

viewing: the display of a motion picture
preview: a screening for a select audience in advance of release for the general public

viewing (noun)	preview (noun)
a vigil held over a corpse the night before burial	a screening for a select audience in advance of release for the general public
the display of a motion picture	an advertisement consisting of short scenes from a motion picture that will appear in the near future

viewing (verb)	preview (verb)
	watch (a movie or play) before it is released to the general public