Definition of spank:
(v) :
to smack or slap a person's
buttocks, with the bare hand or other object, as punishment or as a form of sexual interaction; to soundly defeat, to
trounce
"my father used to put me over his knee and spank my bare bum when I was a bad girl."
(n) :
a slapping sound, as produced by spanking; an instance of spanking; a smack or slap