touch wood

Etymology
From a folk practice of unclear origin.

Verb

 * 1)  To make contact with wood to avert bad luck, in accordance with a folk practice.

Interjection

 * 1)  Hopefully;

Usage notes

 * The expression is used superstitiously to avert the possibility that something just mentioned (if bad) might occur, or (if it is a good thing) might not occur. The action may or may not be performed, depending on how literally the speaker adheres to the superstition. If it is taken literally, it is usual to attempt physically to touch some wooden object whilst, or shortly after, exclaiming touch wood. Failure to find and touch a wooden item within a short time may be considered ominous, and cause mental distress to the person involved.

Etymology
From.

Conjunction

 * 1)  supposing (that something bad happens); what if (something bad happens)