nod

American Heritage® Dictionary of the English Language, Fourth Edition

1. v. To lower and raise the head quickly, as in agreement or acknowledgment.
2. v. To let the head fall forward when sleepy.
3. v. To be careless or momentarily inattentive as if sleepy; lapse: Even Homer nods.
4. v. To sway, move up and down, or droop, as flowers in the wind.
5. v. To lower and raise (the head) quickly in agreement or acknowledgment.
6. v. To express by lowering and raising the head: nod one's agreement.
7. v. To summon, guide, or send by nodding the head: She nodded us into the room.
8. n. A forward or up-and-down movement of the head, usually expressive of drowsiness or agreement: a nod of affirmation.
9. n. An indication of approval or assent: The contestant got the nod from the judges.
10. nod off To doze momentarily: nodded off during the lecture.
11. nod out Slang To fall asleep, especially as a result of taking a drug.

Century Dictionary and Cyclopedia

1. To incline or droop the head forward with a short, quick, involuntary motion, as when drowsy or sleepy; specifically, in botany, to droop or curve downward by a short bend in the peduncle: said of flowers. See nodding, p. a.
2. Figuratively, to be guilty of a lapse or inadvertence, as when nodding with drowsiness.
3. To salute, beckon, or express assent by a slight, quick inclination of the head.
4. To bend or incline the top or part corresponding to the head with a quick jerky motion, simulating the nodding of a drowsy person.
5. To incline or bend, as the head or top.
6. To signify by a nod: as, to nod assent.
7. To affect by a nod or nods in a manner expressed by a word or words connected: as, to nod one out of the room; to nod one's head off.
8. n. A short, quick, forward and downward motion of the head, either voluntary, as when used as a familiar salutation, a sign of assent or approbation, or given as a signal, command, etc., or involuntary, as when one is drowsy or sleepy.
9. n. A quick forward or downward inclination of the upper part or top of anything.

Wiktionary

1. v. transitive and intransitive To incline the head up and down, as to indicate agreement.
2. v. transitive and intransitive to sway, move up and down
3. v. intransitive To gradually fall asleep.
4. v. intransitive To make a mistake by being temporarily inattentive or tired
5. v. intransitive, soccer To head; to strike the ball with one's head.
6. v. intransitive, figuratively To allude to something.
7. v. intransitive, slang To fall asleep while under the influence of opiates.
8. n. An instance of moving one's head as described above.
9. n. A reference or allusion to something.

GNU Webster's 1913

1. v. To bend or incline the upper part, with a quick motion.
2. v. To incline the head with a quick motion; to make a slight bow; to make a motion of assent, of salutation, or of drowsiness, with the head.
3. v. To be careless or inattentive; to make a mistake from lack of attention.
4. v. To be drowsy or dull; to doze off, especially while in a sitting position.
5. v. To incline or bend, as the head or top; to make a motion of assent, of salutation, or of drowsiness with.
6. v. To signify by a nod.
7. v. Poetic To cause to bend.
8. n. A dropping or bending forward of the upper part or top of anything.
9. n. A quick or slight downward or forward motion of the head, in assent, in familiar salutation, in drowsiness, or in giving a signal, or a command.

WordNet 3.0

1. v. let the head fall forward through drowsiness
2. v. express or signify by nodding
3. v. lower and raise the head, as to indicate assent or agreement or confirmation
4. n. a sign of assent or salutation or command
5. v. sway gently back and forth, as in a nodding motion
6. v. be almost asleep
7. n. the act of nodding the head