under the weather vs poorly

under the weather and poorly both are adjectives.

Word	Noun	Adjective	Verb	Adverb
under the weather	No	Yes	No	No
poorly	No	Yes	No	Yes

As adjectives, under the weather and poorly are synonyms defined as:

Other synonyms of under the weather include ailing, indisposed, peaked, seedy, sickly, unwell.

under the weather (adjective)	poorly (adjective)
somewhat ill or prone to illness	somewhat ill or prone to illness

under the weather (adverb)	poorly (adverb)
	(`ill' is often used as a combining form) in a poor or improper or unsatisfactory manner; not well