animal vs big

animal is a noun but big is not a noun.

Word	Noun	Adjective	Verb	Adverb
animal	Yes	Yes	No	No
big	No	Yes	No	Yes

animal (noun)	big (noun)
a living organism characterized by voluntary movement

animal (adjective)	big (adjective)
marked by the appetites and passions of the body	above average in size or number or quantity or magnitude or extent
	conspicuous in position or importance
	given or giving freely
	generous and understanding and tolerant
	marked by intense physical force
	significant
	prodigious
	serious or severe
	loud and firm
	(of animals) fully developed
	in an advanced stage of pregnancy
	feeling self-importance
	exhibiting self-importance