Since a few years I have stopped using (or at least tried to) the word 'design' when it seems more relevant to use the notion of 'designing'. The reason is that I try to be more specific with aspects of design I am addressing.
To me, design is a concept that is broad and extraordinary inclusive. It covers almost anything that has to do with design in all its manifestations and forms. Designing, on the other hand, is more narrow. It is concerned with the practice of design, of the process of design, that is, of design(ing) as an activity.
When it comes to some other similar concepts, such as art and science, the terms are commonly seen as denoting large societal phenomena including their history, present and future. The terms cover all cultural, social, educational, and professional aspects of the phenomena. At the same time, when it comes to the practice or activity the broad terms are no usually used. Instead concepts such as the 'artistic process' or the 'scientific process' are common. Or we talk about 'doing' art or science. The terms science and art are usually not reduced to only signify the practice or process of doing it.
In the same way, the concept of 'design' should be used to denote the larger societal phenomenon of design.
So, why does this matter? Well, if we do want to say specific things about the activity of design, then it seems more appropriate to use the term designing. When people talk about 'design thinking' or 'research through design' it is probably more correct to talk about 'designing thinking' and 'research through designing'. Of course language wise some things have to be changed, not just adding an 'ing'.
The meaning of the 'history of designing' is very different from the history of design. Theory of designing is different from theory of design, etc. I understand that this is minor, minor, thing in the big picture but it matters.
We have many other similar problems in the field of design, for instance with the notion of 'design research' which in some cases means 'the research done by designer during a design process', and in other cases mean ' research about design' and sometimes 'research about designing'. OK, enough...