An Etymological Dictionary of Astronomy and Astrophysics

1. A subtle difference or distinction in expression, meaning, response, etc.
   

2. A very slight difference or variation in color or tone (Dictionary.com).

Etymology (EN): From Fr. nuance “shade of color, hue,” from nuer “to shade,” from nue “cloud,” from L. nubes “a cloud, mist, vapor,” → nebula.

Etymology (PE): Sâgen, from Xoyini sâgené “shade, shadow,” related to sâyé, → shadow.