Nod

(dd) 1 incline one’s head slightly and briefly in assent, greeting, or command. 2 let one’s head fall forward in drowsiness; be drowsy. 3 incline (one’s head). 4 signify (assent etc.) by a nod. 5 (of flowers, plumes, etc.) bend downwards and sway. 6 make a mistake due to a momentary lack of alertness or attention. n. nodding of the head. nod off colloq. fall asleep. [origin unknown]