When after making a remark, you say `touch wood’, you are hoping that the good fortune that you have had so far continues. The expression has the same meaning as `knock on wood’.
*Our wicket keeper hasn’t dropped a single catch all summer. Touch wood. *The second hand scooter I bought recently hasn’t given me any trouble. Knock on wood.
There are several explanations as to the origin of this expression. According to some scholars, it comes from an old superstitious belief that knocking on a tree (wood) helped to drive away evil spirits. Another explanation is that `touch wood’ was the name of a tag game that children played. The aim of the game was to run after your opponents and catch them. But if an individual was touching a tree (wood), then he was safe; he couldn’t be `captured’.