One of its kind (none other has ever existed).
It serves as an intensifier for the number one. Sentences could be just as well understood without it.
Ga' katambahan anaknen, tinggal du dembuwa'-buwa'.
She has no other child; there is just one and only one.
Tinggal dembuwa'-buwa' du Tuhanin.
God is one and only one.
ninggal
Only.
One or one kind of a class of things is left or remains of a collection of similar things. As e.g. one kind of jewelry or building materials. Ninggal is the preferred form though tinggal is possible.
He has sold all materials for the house he was going to build, only posts are left.
ninggal
with the negative existential
None or nothing whatsoever.
None whatsoever of the materials of his house are left.
None whatsoever of her jewelry is left.