Sticking your finger into a womans ass while in doggy style in order to move her forards and backwards with your finger.
"I gave my girl a cornhook from behind and she went crazy!"
by Peter N. Ballsonya June 23, 2003
The cornhook is a manuever performed on women. A finger/fingers are inserted into her butthole and forced into a hook shape that should be viewed by spreading open her pussy lips.
I cornhooked your sister last night.
by Billy America June 23, 2003