Interesting subject that always brings out lots of opinions. Personally, I don't understand the vitriol by some against the term "semi-scale" as applied to model trains. The term makes sense to me, I'll explain why.
First, the definition of the prefix "semi" is not limited to "half of" as in semi-circle. It also can mean partial or quasi Semi | Definition of Semi by Merriam-Webster (merriam-webster.com). The word semiconductor is an example of the prefix semi used in this context.
Second, and more specific to model trains, is this example of my modified MTH RK K4s.
The PSC details added are 1:48 proportioned scale items. Of note, the scale PSC par pilot mated perfectly to the RK pilot beam whish is obviously of scale width. Also interesting is that the RK pilot beam, while of scale width, has a greater than 1:48 scale height to compensate for the too high pilot deck height. MTH RK PRR M1a in the background is another example of a scale pilot added to a model that is not otherwise strictly 1:48 proportioned. So the way I see it, the term semi-scale as applied to O-gauge model trains means that 1:48 scale, selectively compressed, and selectively exaggerated elements are combined to create a caricature of a prototype article that looks and performs well on way too tight (compared to prototype practice) model train curves and turnouts. The context is in keeping with the definition of the prefix "semi."
I don't expect the explanation above to change the minds of semi-scale naysayers, but I hope it clarifies rationale behind the use of the word as I use it to describe my model trains. While I use the the word semi-scale to describe my trains, please don't call them "toys!" 
