a
phrase spoken when one hopes that some misfortune or bad
luck will be prevented,
pass one by or not recur, sometimes accompanied with the
striking of a wooden
object. This
phrase comes from the practice of rapping with one's knuckles on a wooden
object (the
origin of which is uncertain) to avert some impending
evil or
ill twist of
fate, especially after one has stated something has been true up till now and it is hoped it will continue being so. This comes from the
superstition that talking about good
luck, or boasting, might bring bad
luck. The
origin of this belief is uncertain.