nuchal

In the trilobites, relating to the axial segment and groove at the base of the cephalon.

One of two or more plates forming part of the covering of the dorsal portion of the neck in reptiles. The term is usually applied to the well-marked bony plates of crocodiles but also, as in lizards, to horny plates or shields.

Of or pertaining to the nucha or nape: as, the nuchal muscles.

In entomology:

Situated superiorly, just behind the head: said especially of ornaments, processes, etc., on an insect-larva.

Of or pertaining to the metanotal nucha.

Of, pertaining to, or in the region of, the back, or nape, of the neck; — applied especially to the anterior median plate in the carapace of turtles.

The back of the neck

Of or pertaining to the back or nape of the neck.