The most plausible definition I can think of involves stating your metaethics (e.g. utilitarianism) and then showing evidence that there is a reliably-reached c

The most plausible definition I can think of involves stating your metaethics (e.g. utilitarianism) and then showing evidence that there is a reliably-reached conclusion for a claim under those ethics. Like, I don't know: "Under utilitarianism, if you are comparatively rich, it is wrong not to attempt to relieve the suffering of people in extreme poverty, because you can do so very cheaply in comparison to the happiness gain you could cause for other people as rich as you". I'd say that's a moral fact.