“Countervail” developed in Middle English by way of the Anglo-Norman French word “contrevaloir,” which comes from the Latin term “contra valere” (“be of worth against”). The word “countervail” is often used in a metaphorical sense today, as in “offering a countertailing argument,” but the original usage was more literal, in the sense of countervailing weights. In the 16th century, scales became more precise, and medieval merchants needed to be able to accurately measure their goods. They used rocks and other materials as weights to countervail what was being weighed to ensure purchases were fair to both parties.