viewing vs vigil

viewing and vigil both are nouns.

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

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

viewing: a vigil held over a corpse the night before burial
vigil: the rite of staying awake for devotional purposes (especially on the eve of a religious festival)

Other hypernyms of viewing include watch.

viewing (noun)	vigil (noun)
a vigil held over a corpse the night before burial	a purposeful surveillance to guard or observe
the display of a motion picture	the rite of staying awake for devotional purposes (especially on the eve of a religious festival)
	a period of sleeplessness