أو خاصية وهي الغريبة لا يطلع عليها إلا الخاصة
Or the metaphor may be distinctive and unusual, recognized by those with refined understanding.
Khāṣṣiyyah may rest on an unexpected similarity, or on an imaginative linguistic treatment of a likeness already known. Gharībah means rhetorically unusual here; it is not a synonym for using obscure dictionary words.
Unusualness by itself is not excellence. If an expression lacks a recoverable relation between model and target, mere difficulty does not make it an effective metaphor.