What is the real word for God that the word G-d is replacing?
There is no real word. The word is God. G-d is not a word and it doesn't replace the word God. It merely substitutes a hyphen for the letter o. People who use G-d may think they are doing it out of some kind of respect, but all it really is, is a form of conceit.
The word God is used throughout the Bible. Should someone go through the Bible and change the word to G-d throughout? That would be recognized as nonsense. So using G-d instead of God in other written discussions is equally nonsense.
It's like substituting a hyphen for the middle letter in Jesus: Je-us. Dumb, pointless and a silly conceit. How about Holy Trinity: H-ly Tri-ity. Or Christ: Ch-ist. Makes a mockery out of the words and names, all for the sake of someone trying to prove a point about themselves. The very definition of conceit.