Knowledge is not only about accurate answers, it is also the capacity to comprehend situations and the ability to explain convictions. With sufficient knowledge, one can make informed choices. Euthypro prosecuted his father because he believed that to prosecute a wrongdoing was holy. Socrates doubted Euthypro fully knows what holiness meant so he engaged Euthypro in a discussion. Euthypro muddled with his answers, so Socrates knew that Euthypro knew basically nothing about holiness.
One mans meaning is not a barometer for the true and accurate definition of holiness. Still, with mans limited means and imperfections as we were not created with infinite knowledge, we can only go by with what our capabilities and abilities permit. Holiness to one may only be slightly holy to another and may not be holy at all to yet another. Going by the premise of Plato that holiness has no meaning if it can not be defined, could also mean that holiness is a personal thing. How one defines it, his understanding and stand on holiness is what holiness is to him.
Reconciling that with the what the others mean about holiness must be left to the authorities. In the time of Euthypro and Socrates, the final arbiter was Zeus. Today, church scholars and government legislators are the authors of our laws. It is their definition and meaning that must be followed and believed to be right. The learned and the unschooled, each have their own definition and meaning of holiness. This is accepting of the truth in Platos premise that holiness has no meaning unless we can define it.