A note about the use of the terms "figure" and "grain", how I use them and how Dr. Hoadley uses them and the justification for my own point of view over his.
First, my purpose in providing this glossary is NOT to validate (or invalidate) any academic points of view. I don't really care about academic points of view. My entire and only goal is to provide information that is useful to wood craftspeople in the USA. From THAT point of view, my interpretation of the "correct" use of grain and figure IS in fact the correct one because it is the overwhelming consensus point of view of the English speaking world. More on that below.
Second, what IS my point of view and that of Dr. Hoadley? Here's the deal: the term grain is used in two ways in relation to wood. The first way implies having to do with the growth rings of a tree and the pores along those growth rings. In this form of usage, and this is about 80% of the ways that he shows the word grain used, I am in total agreement with Dr. Hoadley (and in fact, as far as I am aware, so is EVERYONE). The second form of useage implies having to do with wood appearance in ways that are only secondarily related to, or almost UNrelated to, the rings and pores. Such usage should, I believe, substitute the word "figure" for the word "grain". A blatant example of this is "bird's eye". To me, this is a wood figure, not a wood grain. To me, the phrase "bird's eye grain" is screechingly awful and makes the hair on the back of my neck stand up, whereas term "bird's eye figure" rolls off the tongue smoothly.
Dr. Hoadley, in "Understanding Wood", presents a table of usage of the term grain and in that table he has a subset of "figure type" which includes "bird's eye grain", "roey grain", and so forth. For items such as roey and fiddleback and others that he presents as "grain" types, I take the point of view that these are descriptions of wood figure that are a RESULT of some form of grain but are not themselves grain terms. That is, I say that roey and fiddleback are not types of grain, they are types of figure, whereas Dr. Hoadley's table puts them as types of grain. To me, figure is a broad term that encompasses all of the characteristics that go into the formation of a wood's appearance and grain is just one of those characteristics and it is limited to things directly and specifically related to tree rings and pores. That is the way I use the terms in this glossary. I belive a fair analogy would be to say that the rubber from car tires should be described as either "tire rubber" or "car rubber". There is an undeniable connection between the tire and the car, but the phrase "car rubber" just sounds silly in the same way that I think "bird's eye grain" sounds silly.
Fortunately for my sanity (and the hair on the back of my neck), my point of view is very widely shared, to the point where I can safely say that it is the current consensus among English-speaking woodworkers. How do I know this? Well, there is a facility available today to sample opinion in a way that was not available to Dr. Hoadly back when he was compiling his information on wood. It's the internet. I googled the compound phrases "bird's eye grain" (with the quotes) and "bird's eye figure", and a couple of similar phrases.
In every case, the number of hits with the word figure was over 70% of the total hits for both forms and in one case it was over 90%. This is an obvious concensus towards the use of figure and grain in the way that I present them in this glossary. Here are the stats:
"bird's eye grain": 794 hits
"birdseye grain": 519 hits
grain total: 1313 (25% of the total "grain vs figure" hits)
"bird's eye figure": 800 hits
"birdseye figure": 2990 hits
figure total: 3970 (75% of the total "grain vs figure" hits)
fiddleback grain: 492 (29%)
fiddleback figure: 1220 (71%)
roey grain: 425 (8%)
roey figure: 4830 (92%)
So, am I saying that common usage trumps academic expertise? In this case, yes I am. Over time, common usage BECOMES the "correct" definition of terms. Word usage in all languages, and I would argue that this is especially true in English, is a process of evolution.