week vs period of time

week and period of time both are nouns.

Word	Noun	Adjective	Verb	Adverb
week	Yes	No	No	No
period of time	Yes	No	No	No

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

Other hypernyms of week include period, time period.

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

week: a period of seven consecutive days (usually reckoned to be from Sunday to Saturday, or from Monday to Sunday)
period of time: an amount of time

Other hypernyms of week include period, time period.

week (noun)	period of time (noun)
any period of seven consecutive days	an amount of time
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)