period vs period of time

period and period of time both are nouns.

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

As nouns, period and period of time are synonyms defined as:

Other synonyms of period include time period.

period (noun)	period of time (noun)
a punctuation mark (.) placed at the end of a declarative sentence to indicate a full stop or after abbreviations	an amount of time
the monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause
an amount of time
the interval taken to complete one cycle of a regularly repeating phenomenon
a unit of geological time during which a system of rocks formed
the end or completion of something
(ice hockey) one of three divisions into which play is divided in hockey games