What's "sound" mean here? And in what context can it be used in this way?

Native speaker’s answer
Rebecca
Good question! In this context, "sound" is an adjective meaning based on logic, reason, or judgement. Thus, "morally-sound" means to be logical or reasonable according to common morals. Ex: It's not morally-sound to force people to do things they don't want to. Ex: Their argument is not logically sound, so we ignored them.