وَلَوْ لِاعْتِقَادِ الْمُخَاطَبِ بِعُرْفٍ
Even if the relevant connection is established for the hearer through customary understanding.
General usage is what ordinary members of a linguistic community recognize. Specialized usage belongs to a discipline, profession, or group. In bayān, the listener's competence matters because a link that is immediate to an expert may remain obscure to someone outside that circle.
For example, “rafʿ” can refer generally to raising, whereas in grammatical discourse it also identifies the nominative state. This illustrates how knowledge of a field shapes interpretation. It does not mean that an arbitrary private association becomes a valid linguistic entailment.