Originally Posted by
Allan Lupton
What I have heard of is the Sopwith "1½ Strutter" which I expect was named after an unusual arrangement of struts in the wing installation. Perhaps someone can explain what a "strutter" is supposed to be.
I think you are looking for meaning where none exists - "1½ Strutter" was indeed a reference to the upper wing being attached by a combination of long and short struts, no more than that. I suspect that the unofficial name proved more convenient than referring to it as the Sopwith Two-Seater (some variants were in fact single-seaters).
A similar more recent usage would be describing the 727, TriStar, etc as a "3 holer".