Sound a little strange, doesn’t it? 
Here’s some examples:
So “pneumatic” is an adjective, not a noun. It’s used to describe the type of cylinder in a fluid power system, i.e. “pneumatic cylinder” or “hydraulic cylinder.” I will say it’s a step up from calling air cylinders “pistons.” (If you’re going to call your air cylinders “pistons” then you should call your motors “armatures” for consistency, since we’re referring to the small moving part within the unit.)
As someone who is both an engineer and educator, I’d encourage students to learn proper terminology when discussing technical stuff. Outside of the student-robotics-world, such as every technical manual, catalog, manufacturer’s website, etc, these actuators are always called air cylinders or pneumatic cylinders.
It’s also easier to spell:
