It seems that inch and ounce are related. The Latin uncia, meaning "twelfth part", was apparently borrowed into early Old English as unkja, which became ynch. The word was borrowed again a few centuries later from postclassical Latin and Middle French as unce or ounce. The Latin uncia comes from unus, meaning "one". I don't know Latin well enough to how unus + cia = "one twelfth".