effort vs least effort

effort and least effort both are nouns.

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

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

effort (noun)	least effort (noun)
earnest and conscientious activity intended to do or accomplish something	the least effortful way to do 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