Precambrian vs Precambrian eon

Precambrian and Precambrian eon both are nouns.

Word	Noun	Adjective	Verb	Adverb
Precambrian	Yes	No	No	No
Precambrian eon	Yes	No	No	No

As nouns, Precambrian and Precambrian eon are synonyms defined as:

Precambrian and Precambrian eon: the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago

Other synonyms of Precambrian include Precambrian aeon, Precambrian period.

Precambrian (noun)	Precambrian eon (noun)
the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago	the eon following the Hadean time and preceding the Phanerozoic eon; from about 3,800 million years ago until 544 million years ago