وحكم المشترك: أنه إذا تعين الواحد مرادًا به سقط اعتبار إرادة غيره
Once one of the meanings of a homonymous expression is established as intended, the other is no longer treated as simultaneously intended by that same occurrence.
The rule concerns what the speaker intends in a particular utterance. One cannot add another independent lexical sense to that utterance without a separate basis.
If al-mushtarī is clearly the buyer in a sales contract, no ruling about the planet Jupiter can be extracted from the same usage.
The selection must rest on evidence for the intended sense, not a reader's arbitrary preference.