A quick definition of gainage:

Gainage: A word that means the same thing as "wainage" and refers to the amount of grain or other crops that a farmer is able to harvest. It can also refer to having a job that pays well, which is called "gainful employment." Another word that means the same thing as gainage is "gainor," which is another word for a wealthy landowner. Gains is a plural word that means the same thing as gain, which is when you make a profit or earn something valuable. Gal is an abbreviation that stands for "guardian ad litem," which is a person who is appointed by a court to represent the interests of a child or other vulnerable person in legal proceedings. Gale is a historical term that refers to a type of rent that was paid by miners for the right to mine a plot of land.