elbow grease

Strenuous physical labor and effort.

noun

The use of energy to do something: effort, endeavor, exertion, pain (used in plural), strain¹, striving, struggle, trouble, while. See work/play.

Strenuous physical effort, as in You'll have to use some elbow grease to get the house painted in time. This term alludes to vigorous use of one's arm in cleaning, polishing, or the like. It soon was extended to any kind of hard work, and Anthony Trollope used it still more figuratively (Thackeray, 1874): "Forethought is the elbow-grease which a novelist ... requires." [First half of 1600s]

The noun has one meaning:

Meaning #1: use of physical or mental energy; hard work
  Synonyms: effort, exertion, travail, sweat

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