I think that the root k-b-r is best to translate understood from English "gross". It can describe something big, huge and also some be opposite of "net amount". Thus, especially causative verb forms (II and V) can be used to describe somebody/something from whom nothing is deducted or can't be deducted, its net value is same as gross value. In relation to Allah, this would mean that nothing can be taken from Him because He didn't add anything out of Himself. For example, if we put some goods in some container it will have its new gross mass, which is its net mass + mass of the container.