الاستخدام: وهو أن يراد بلفظ له معنيان أحدهما ثم يراد بضميره معناه الآخر
Istikhdām uses an expression with two meanings, intending one sense in the explicit word and the other through a pronoun referring back to it.
The decisive element is the shift in the sense represented by the overt word and by its referring pronoun. There is grammatical continuity but not identical semantic reference.
The second sense must be warranted by the context. An ordinary pronoun returning to the same meaning does not constitute istikhdām.