2. A glove or other object that is thrown down or offered as a challenge to fight: The knight hurled his scarf down at the feet of the other warrior as a gage to confront him in a duel.
2. Measuring instrument, measuring device, standard, criterion: This gauge registers the pressure in pounds.
3. Size, measurement, internal diameter, inner measurement, inner dimension: What gauge is that cannon?
In the sense of "measurement", gauge is the preferable spelling. With the meaning of "a pledge", gage is the correct and preferred form.
In order to gauge his sincerity, she asked him to leave a gage in her safekeeping. This was the equivalent of the gage often referred to in romantic medieval ballads either when the princess could gauge the affections of the knight by the gage he left her or when a knight would throw his glove or gage to the ground to challenge an opponent.
2. The general name for an instrument which measures the evaporation rate of water into the atmosphere.