I'd like to know if thing is the most general in meaning among the nouns. In other words, is there an entity that can not be called as a thing? I know being refers to all the lives (animals and plants), substance can refer to all the materials in the world, and idea refers to pieces of thought in the mind. But lives, substances and ideas can all be called things.
For example, if we want to find a word for all entities in the world with the white color, we can say the everything is white, or snow is white, where white is adjective and the object is known as a subject complement. But what is for noun? Can we say that snow is a white thing? Of course, we can say that snow is a white substance. In addition, we can say a polar bear is white or a polar bear is a white being. But can we say a polar bear is a white thing?
Generally, this relies on whether a subject complement can always be replaced by a noun (phrase). If so, thing is (probably) the best candidate of noun to be used.