nod 
(nŏd)
(nŏd)v. nod·ded, nod·ding, nods
v.intr.
1. To lower and raise the head quickly, as in agreement or acknowledgment.
2. To let the head fall forward when sleepy.
3. To be careless or momentarily inattentive as if sleepy; lapse: Even Homer nods.
4. To sway, move up and down, or droop, as flowers in the wind.
v.tr.
1. To lower and raise (the head) quickly in agreement or acknowledgment.
2. To express by lowering and raising the head: nod one's agreement.
3. To summon, guide, or send by nodding the head: She nodded us into the room.
n.
Phrasal Verbs: 1. A forward or up-and-down movement of the head, usually expressive of drowsiness or agreement: a nod of affirmation.
2. An indication of approval or assent: The contestant got the nod from the judges.
3. Informal A nomination for an award.
nod off
To doze momentarily: nodded off during the lecture.
nod out Slang
To fall asleep, especially as a result of taking a drug.
[Middle English nodden; perhaps akin to Middle High German notten.]
nodder n.