be sick vs sick

be sick is not a noun while sick is a noun.

Word	Noun	Adjective	Verb	Adverb
be sick	No	No	Yes	No
sick	Yes	Yes	Yes	No

As verbs, be sick and sick are synonyms defined as:

be sick (noun)	sick (noun)
	people who are sick

be sick (adjective)	sick (adjective)
	affected by an impairment of normal physical or mental function
	shockingly repellent; inspiring horror
	having a strong distaste from surfeit
	affected with madness or insanity
	deeply affected by a strong feeling
	(of light) lacking in intensity or brightness; dim or feeble
	feeling nausea; feeling about to vomit

be sick (verb)	sick (verb)
eject the contents of the stomach through the mouth	eject the contents of the stomach through the mouth