Angie has helped me twice with understanding the current usage of terms whose meanings have shifted over time. If not for that I'd be going crazy wishing people were using terms "correctly."
The first is "midi." When midis came in in the 70s, the term meant roughly mid-calf. Now, as Angie explained again today, midis start at the bottom of the knee! This usage is taking me a while to get used to.
Another is "A-line." When I was in seventh grade taking sewing, as all girls were required to do back then (the boys took woodshop), the first garment I sewed was an A-line skirt. This was a very specific garment that fit smoothly around the waist and high hip and then gently slanted out to just a few inches wider than a pencil skirt. Now the term is also used to describe any kind of skirt wider than a pencil even if it's pleated or gathered or flared (none of which happens with a traditional A-line).
Any other style-related terms that mean something different than what they used to?