Wiktionary
touch wood
interj. (context idiomatic UK Australia New Zealand English) hopefully; ''said while touching something wooden, to avert superstitious bad luck from what has just been said''. vb. To make contact with wood to avert bad luck, in accordance with a folk practice.
Usage examples of "touch wood".
They would not touch wood or any fossil fuel, because the wood was too valuable for other purposes and the others were nonrenewable and polluting.