There’s a nice new, short and to the point, video from Venaloid looking at the definitions of atheism and theism.
Language often breaks down when discussing sensitive topics, in particular because the way we use words in conversation can drift over time and between groups. So a word may not mean quite the same thing as its dictionary definition, or might not mean the same thing as you would infer simply from analyzing the root words. The simplest example might be words like “wicked” or “terrific”, which are now used as positive, but historically have some severely negative connotations.
The important part is the scientific idea of the “null hypothesis”, which is a relatively new philosophical concept, is hard to accommodate because we tend to default to binary, either/or thinking and finding words to occupy the reasonable middle ground can be a challenge.
I found the video to be very thoughtful. The only thing I would object to is that anti-theist is already in use, popularized by the late Christopher Hitchens. To him an anti-theist was someone who, separate from believing in god/s, believes that the godless universe is morally superior. He was famous for his analogy that theism, taken sincerely, was like a fantasy North Korea, and not something to be desired.