application vs elbow grease

application and elbow grease both are nouns.

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

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

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

application (noun)	elbow grease (noun)
the action of putting something into operation	use of physical or mental energy; hard work
a diligent effort
the act of bringing something to bear; using it for a particular purpose
the work of applying something
liquid preparation having a soothing or antiseptic or medicinal action when applied to the skin
a verbal or written request for assistance or employment or admission to a school
a program that gives a computer instructions that provide the user with tools to accomplish a task