shiva vs week

shiva and week both are nouns.

Word	Noun	Adjective	Verb	Adverb
shiva	Yes	No	No	No
week	Yes	No	No	No

As nouns, week is a hypernym of shiva; that is, week is a word with a broader meaning than shiva:

shiva: (Judaism) a period of seven days of mourning after the death of close relative
week: any period of seven consecutive days

Other hypernyms of shiva include hebdomad.

shiva (noun)	week (noun)
(Judaism) a period of seven days of mourning after the death of close relative	any period of seven consecutive days
	hours or days of work in a calendar week
	a period of seven consecutive days (usually reckoned to be from Sunday to Saturday, or from Monday to Sunday)