The source uses Abdullah as a proper name. Abd and Allah are meaningful elements in ordinary language, yet when Abdullah identifies a particular person, those elements are not being used to signify distinct parts of that person. The entire expression functions as one name. In that naming use, it is mufrad despite its meaningful constituents.
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Third form: meaningful parts within a single proper name
Simple and Composite Expressions: Definitions, Four Forms, and Examples
The source uses Abdullah as a proper name. Abd and Allah are meaningful elements in ordinary language, yet when Abdullah identifies a particular person, those elements are not being used to signify distinct parts of that person. The entire expression functions as one name. In that naming use, it is mufrad despite its meaningful constituents.