struggle vs elbow grease

struggle and elbow grease both are nouns.

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

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

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

struggle (noun)	elbow grease (noun)
strenuous effort	use of physical or mental energy; hard work
an energetic attempt to achieve something
an open clash between two opposing groups (or individuals)

struggle (verb)	elbow grease (verb)
be engaged in a fight; carry on a fight
to exert strenuous effort against opposition
climb awkwardly, as if by scrambling
make a strenuous or labored effort