1. Insusceptible of being measured by the same criteria as something else: Perhaps the differences between meat and fruit are so great that they can be considered to be incommensurable.
2. Not deserving comparison: The statement that Bob uttered was incommensurable with the truth of how the incident happened.
3. Not possessing units of the same dimension: Perhaps it can be said that temperatures expressed in Celsius are incommensurable with the Fahrenheit system of defining temperatures.