least effort vs effort

least effort and effort both are nouns.

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

As nouns, effort is a hypernym of least effort; that is, effort is a word with a broader meaning than least effort:

Other hypernyms of least effort include elbow grease, exertion, sweat, travail.

least effort (noun)	effort (noun)
the least effortful way to do something	earnest and conscientious activity intended to do or accomplish something
	use of physical or mental energy; hard work
	a notable achievement
	a series of actions advancing a principle or tending toward a particular end