Definition of twock:
(n) :
(uncommon) The sharp, quick sound of one hard thing hitting another hard (or rubber or leather) thing, especially sports equipment such as a bat hitting a ball.
(n) :
(uncommon) A twang; the sharp, quick sound an arrow being shot (and a bowstring vibrating) or hitting something hard.
(v) :
Alternative form of twoc. [(UK regional, slang) To steal (especially a car).]