ولو عنى بالملك الشراء، أو بالشراء الملك صحت نيته بطريق المجاز
The relationship between purchase and ownership can justify a transferred meaning when the speaker intends the related legal concept.
One may use the language of ownership while intending the act of purchase, or the language of purchase while intending its resulting ownership. Their cause-and-effect relation makes the transfer intelligible.
This does not mean that private intention can assign any meaning to any word. A recognized connection, the situation of utterance, and applicable legal conditions remain decisive.