Al Baatin

Baṭn is a belly, the inside of a thing, and bāṭin is whatever lies under the surface. From the same root comes biṭāna, the lining of a garment — which the Qur’an uses for the close friend who knows your private business, the person on the inside.

It closes the four names of that ayah in Sūrat al-Ḥadīd, immediately after aẓ-Ẓāhir, and the two are set next to each other rather than against each other. Things you cannot see are not thereby absent.