وَغَيْرُ مُنْصَرِفٍ: وَهُوَ مَا فِيهِ سَبَبَانِ مِنَ الْأَسْبَابِ التِّسْعَةِ، أَوْ وَاحِدٌ مِنْهُمَا يَقُومُ مَقَامَهُمَا.
Translation: A ghayr munṣarif is a noun containing two of the nine causes, or one cause considered equivalent to two.
A diptote is still muʿrab, not mabnī. But its normal genitive ending and its treatment of tanwīn differ from a munṣarif noun.