Nuchal means "on the nape."
"The Woodpeckers"
Fannie Hardy Eckstorm
The lips are dark brown, with two streaks up to the small spines on the forehead; there is a dark cross-band from the base of the two large horns over the eyebrows, running behind, and then dividing into broad streaks, one along each side of the centre of the back of the neck to between the shoulders, crossing the Nuchal swelling.
"Journals Of Two Expeditions Of Discovery In North-West And Western Australia, Vol. 2 (of 2)"
George Grey
4. A scarlet Nuchal crescent 4. No Nuchal crescent in in both sexes.
"Hormones and Heredity"
J. T. Cunningham