In Judaism the four Hebrew letters (referred to as the Tetragrammaton) that spell out the name of G-d are NEVER pronounced. We say Adonai, The Lord, or other substitutes when it appears in the liturgy. Why?
It is referred to by the Rabbis I have known as the Ineffable Name of G-d. But the real reason I have been told is that if you can NAME something, it is finite. G-d is not. I am not necessarily superstitious, but the idea appeals to me. Enjoy the link.
in·ef·fa·ble
/inˈefəb(ə)l/
adjective
- too great or extreme to be expressed or described in words.