the world > movement > motion in specific manner > alternating or reciprocating motion > move to and fro or up and down [verb (transitive)] > nod the head (5)
transitive. To incline (the head) briefly in a nod. Also in extended use.
transitive. To shake, nod (the head). Obsolete.
transitive. To nod (the head) quickly or slightly. Now English regional (northern).