Definition of "Nod" :
noun: the act of nodding the head
noun: a sign of assent or salutation or command
verb: be almost asleep
"The old man sat nodding by the fireplace."
verb: let the head fall forward through drowsiness
"The old man was nodding in his chair."
verb: lower and raise the head, as to indicate assent or agreement or confirmation
"The teacher nodded when the student gave the right answer."
verb: express or signify by nodding
"He nodded his approval."
verb: sway gently back and forth, as in a nodding motion
"The flowers were nodding in the breeze."