Taḍammun (التضمن) concerns a constituent already included in the meaning established for a word. In traditional analysis, the concept “human” contains such components as living being and rationality; indicating one constituent is inclusion rather than indication of the full definition.
A constituent need not be a detachable physical piece. Conceptual definitions have analyzable parts: rationality is a component of the intended conception, not a physical fragment of the person.
An important limitation is that an accidental property is not automatically an internal component. People can write or run, but writing and running are not, merely for that reason, constituents of the definition of “human.” The category depends on conceptual inclusion.