In short, “chas v’shalom” is a Hebrew phrase that means “G-d forbid.” The Aruch HaShulchan says that it should be literally translated as “completely disgraced.” (“Shalom,” peace, literally means complete or whole.)
Three year old to his two year old brother: “Isn’t it great?! Grandma is going to bring me LOTS of gluesticks! That way, in case one chas v’shalom runs out, we’ll have another one!”
“You know, mom, I might not get into Yale…”
“Chas v’shalom!”
As you begin to see above, the phrase can be inserted anywhere in the sentence. It can even be used as its own sentence! I’ll avoid boring you with describing the different grammatical structures you might see. As you hang out with more orthodox Jews, you will get a feel for how to use it yourself. Thankfully (because of its grammatical flexibility), it’s pretty hard to mess up if you think of it as “G-d forbid!”
Note: It is equally acceptable to say “G-d forbid!” in English. Thankfully, American English speakers don’t think you’re weird for saying it either.
Was does Chas mean alone?
It is a request to the Almighty for "mercy and peace."
Where does the Shulchan Arukh gives that definition?
שלום וברכה