1610s, "action of nodding," from Latin nutationem (nominative nutatio), noun of action from past participle stem of nutare "to nod," from PIE *neu- "to nod" (see numinous). Astronomical use is from 1715. Related: Nutational.
nutation nu·ta·tion (nōō-tā'shən, nyōō-)
The act of nodding the head, especially involuntarily.