For something to be described as moribund it must have ceased to be useful, in the act of dying, or close to be obsolete. The noun form is moribundity.
It comes from the Latin moribundus with the same meaning. Unlike morbid, which comes from the Latin morbidus or diseased.
According to Google’s ngram, moribund has only slightly fallen from its peak of popularity in the 1970’s.