Merriam-Webster's Collegiate® Dictionary, 11th Edition
STUN
I. transitive verb (stunned; stunning) see: astonish
Date: 14th century
to make senseless, groggy, or dizzy by or as if by a blow ; daze , to shock with noise, to overcome especially with paralyzing astonishment or disbelief,
II. noun
Date: 1727
the effect of something that stuns ; shock