Commensurability

“Commensurability” refers to the property of being defined by compatible units. For instance, the length of my toothbrush is commensurable with the distance between the Earth and the Moon–you can measure both in inches, or meters, or whatever–whereas the length of my toothbrush is incommensurable with the temperature of the room you are in right now—it makes no sense to speak of the length of your toothbrush in degrees Celsius or the temperature of your room in feet.