effort vs mug's game

effort and mug's game both are nouns.

Word	Noun	Adjective	Verb	Adverb
effort	Yes	No	No	No
mug's game	Yes	No	No	No

As nouns, mug's game is a hyponym of effort; that is, mug's game is a word with a more specific, narrower meaning than effort:

effort: earnest and conscientious activity intended to do or accomplish something
mug's game: a futile or unprofitable endeavor

effort (noun)	mug's game (noun)
earnest and conscientious activity intended to do or accomplish something	a futile or unprofitable endeavor
use of physical or mental energy; hard work
a notable achievement
a series of actions advancing a principle or tending toward a particular end