I actually came across the word plenum in my automotive world first. There's a spacer between the intake funnel, and the throttle body. That's referred to as a plenum.
Not long after I got a job installing networking cable in a school. They told me I needed plenum wire. That didn't make any sense at all, because I knew, from context, that a plenum had something to do with the intake on a car.
So to have the two worlds meet up on my head I had to find the root of the meaning. After that I've always insisted on the correct usage.
