Er vs erbium

Er and erbium both are nouns.

Word	Noun	Adjective	Verb	Adverb
Er	Yes	No	No	No
erbium	Yes	No	No	No

As nouns, Er and erbium are synonyms defined as:

Er and erbium: a trivalent metallic element of the rare earth group; occurs with yttrium

Other synonyms of Er include atomic number 68.

Er (noun)	erbium (noun)
a trivalent metallic element of the rare earth group; occurs with yttrium	a trivalent metallic element of the rare earth group; occurs with yttrium