effort vs difficulty

effort and difficulty both are nouns.

Word	Noun	Adjective	Verb	Adverb
effort	Yes	No	No	No
difficulty	Yes	No	No	No

As nouns, difficulty is a hyponym of effort; that is, difficulty is a word with a more specific, narrower meaning than effort:

effort (noun)	difficulty (noun)
earnest and conscientious activity intended to do or accomplish something	an effort that is inconvenient
use of physical or mental energy; hard work	the quality of being almost beyond one's ability to deal with and requiring a great effort to achieve a positive result
a notable achievement
a series of actions advancing a principle or tending toward a particular end