Knock on wood is an expression used to express HOPE or to ward off bad luck. It is believed to have originated from the superstition that knocking on wood will bring good luck and ward off bad luck. The crossword solutions for the term Knock on Wood are RAP (3 letters) and HOPE (4 letters). RAP stands for Rhythm and Poetry, which is a form of music that combines spoken word and rhythm. HOPE stands for Helping Other People Everywhere, which is a phrase used to express the idea of helping people in need.