Ordovician vs Ordovician period

Ordovician and Ordovician period both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ordovician	Yes	No	No	No
Ordovician period	Yes	No	No	No

As nouns, Ordovician and Ordovician period are synonyms defined as:

Ordovician and Ordovician period: the period from 500 million to 425 million years ago; characterized by conodonts and ostracods and algae and seaweeds

Ordovician (noun)	Ordovician period (noun)
the period from 500 million to 425 million years ago; characterized by conodonts and ostracods and algae and seaweeds	the period from 500 million to 425 million years ago; characterized by conodonts and ostracods and algae and seaweeds