overexertion vs elbow grease

overexertion and elbow grease both are nouns.

Word	Noun	Adjective	Verb	Adverb
overexertion	Yes	No	No	No
elbow grease	Yes	No	No	No

As nouns, elbow grease is a hypernym of overexertion; that is, elbow grease is a word with a broader meaning than overexertion:

overexertion: excessive exertion; so much exertion that discomfort or injury results
elbow grease: use of physical or mental energy; hard work

Other hypernyms of overexertion include effort, exertion, sweat, travail.

overexertion (noun)	elbow grease (noun)
excessive exertion; so much exertion that discomfort or injury results	use of physical or mental energy; hard work