nod

[1]	greet , acknowledge , recognize
[2]	say yes , consent , assent , agree , concur , acquiesce
[3]	doze (off) , nap , drowse , drop off , fall asleep
[4]	slip (up) , err , make a mistake , be mistaken/wrong , be careless/negligent/lax/inattentive

[1]	signal , sign , cue , indication , gesture
[2]	approval , consent , acquiescence , concurrence , assent , agreement , (Colloq) OK/okay