1
general::
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]
American Heritage Idioms
2
general::
Phrase(s): elbow grease
Fig. hard scrubbing. • Tom: What did you use to get your car so shiny? Mary: Just regular wax and some elbow grease. • Joe put a lot of elbow grease into cleaning the kitchen.
McGrawhill's American Idioms And Phrasal Verbs