to nod is a form of:

Persistency



ENGLISH MEANING
noun
1.
The quality or state of being persistent; staying or continuing quality; hence, in an unfavorable sense, doggedness; obstinacy.
2.
The continuance of an effect after the cause which first gave rise to it is removed
3.
The persistence of motion.
4.
Visual persistence, or persistence of the visual impression; auditory persistence, etc.