I suppose "old fashioned" is much more of a subjective measurement than an objective one. At first I was going to rate "snail" as not at all old fashioned, since we still use the word. But then, I thought of medieval snail drawings, and felt like the word has some element to it that does harken back to older days. "Citadel" is kind of a similar example. There is a modern hedge fund named Citadel and we still use that word, but it also has a connection to the past. I'd say Citadel is more "old timey" than "snail" even though both words are in modern parlance.
A better way to think about it is that these measurements are my subjective opinion on old timeyness and sillyness via an undefined and intuitive process for assigning values.
> like the word has some element to it that does harken back to older days
It's more interesting than you might think! Turns out snail is a diminutive form of snake[1], from a root referring to creeping over the ground.
The other aspect of judgments of old-fashionedness is that things that are really old-fashioned, like being named Etheldreda, will tend to be rated as less old-fashioned than things that are pretty recent but out of current fashion, like being named Gertrude. The old old things are too forgotten to be "old".
My other question would be "why 'cosine similarity' rather than 'correlation'?". Same thing, but people are a lot more familiar with the term 'correlation'.
[1] OE snaca preserved the /k/ sound, but OE snægl voiced it, and the /g/ then predictably turned into a Y sound (compare "yard" / "day"), giving us the I of modern snail.
A better way to think about it is that these measurements are my subjective opinion on old timeyness and sillyness via an undefined and intuitive process for assigning values.