difficult vs complex

difficult is not a noun while complex is a noun.

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

difficult (noun)	complex (noun)
	a whole structure (as a building) made up of interconnected or related structures
	a conceptual whole made up of complicated and related parts
	(psychoanalysis) a combination of emotions and impulses that have been rejected from awareness but still influence a person's behavior
	a compound described in terms of the central atom to which other atoms are bound or coordinated

difficult (adjective)	complex (adjective)
not easy; requiring great physical or mental effort to accomplish or comprehend or endure	complicated in structure; consisting of interconnected parts
hard to control	difficult to analyze or understand