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.