Would you please define material?
Typically, dictionaries say:
Material Adj. Of, relating to, or composed of matter.
A car is regarded as material since it is made of matter though it has also a shape, a structure, a functionning etc. Shapes, structures, functionnings etc. are not made of matter but are regarded as material properties since they don't appear without some quantity of matter (words too). A ghost, if immaterial, would have, say, shape, perhaps movement, possibly colours, but not matter.
So things that exist would be immaterial if and only if they didn't need to be asociated with matter. Since shapes, structures, functionnings and indeed words are always associated with matter they are said to be material.
That being said, to say that the mind is immaterial makes sense. It means that you believes that the mind can exist without any matter associated with it, as indeed many people seem to believe.
However, I fail to see the point of arguing that shapes, structures, functionnings or indeed words etc. are immaterial. They are not made of matter, we all agree with that, but they always come with matter associated with them. We could not perceive them if they didn't come with matter associated with them. Even our mind does. Unless you can find an example.
EB