But... I mean, if you asked 100 people what they think a spectrum means in this context, how many of them would think it meant "vector" rather than "real number"? I would guess fewer than 10. I consider myself a fairly well-informed nerd, but I think I had encountered many usages of "spectrum" describing a single trait for many years, and I think this is the second time I've ever encountered someone using the "vector" definition (the first one was also using it to describe autism). Has this linguistic battle already been lost? Does it improve clarity to call it a "spectrum" and insist on using the "vector" definition?
(I've personally been using the phrase "collection of imperfectly correlated traits")