preview vs viewing

preview and viewing both are nouns.

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

As nouns, viewing is a hypernym of preview; that is, viewing is a word with a broader meaning than preview:

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

Other hypernyms of preview include screening, showing.

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

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