difficult vs tough

difficult is not a noun while tough is a noun.

Word	Noun	Adjective	Verb	Adverb
difficult	No	Yes	No	No
tough	Yes	Yes	No	No

difficult (noun)	tough (noun)
	an aggressive and violent young criminal
	a cruel and brutal fellow
	someone who learned to fight in the streets rather than being formally trained in the sport of boxing

difficult (adjective)	tough (adjective)
not easy; requiring great physical or mental effort to accomplish or comprehend or endure	resistant to cutting or chewing
hard to control	physically toughened
	not given to gentleness or sentimentality
	unfortunate or hard to bear
	substantially made or constructed
	feeling physical discomfort or pain (`tough' is occasionally used colloquially for `bad')
	violent and lawless
	very difficult; severely testing stamina or resolution
	making great mental demands; hard to comprehend or solve or believe