The `ex’ is pronounced like the letter `x’, and the following `o’ is like the `ou’ in `ought’, `sought’ and `fought’. The final `ism’ sounds like the `ism’ in `prism’. The main stress is on the first syllable. When you `exorcise’ a ghost or an evil spirit, what you do is to drive it away by making use of magic or prayers. This act of driving away an evil spirit is called `exorcism’.
Example: The witch doctor tried to exorcise the evil spirit from the library.