The typical life span of a word is what, a few centuries? Function versus content, open versus closed class, part of speech all certainly affect the distribution in interesting ways, but lexical items are, on average, long-lived human creations. They leave corporations, nations, and individual human beings literally in the dust. How widespread is a typical word? By definition, the majority of a language must be known to the majority of its speakers, so the name recognition of a mid-range lexical item in a major language will far outstrip that of all but the biggest celebrities.
What are the edge cases? Cultural and technological ephemera–I doubt “Betamax” and “Pong” will persist to the end of the current century as anything but O.E.D. curiosities. Some slang ossifies into regular speech, but other slang shines brightly for a moment then turns to air. I’m betting “gnarly” has already gone the way of the dodo. Along the speaker-count axis we have professional jargon, technical terms, medical Latin, and polysyllabic biochemical jawbreakers. Also, situation-specific terms. At my high school in suburban Philadelphia in the late 1980s the interjection “Face!” was something you chirped out when someone had just been humiliated–as in lost face, I guess. I’ve never been clear whether that was a regionalism or just a private joke. We can chase this all the way down to family nicknames. At the low end, though, we’re still talking decades and tens of people.
Now say you’re painting your den. You go to the paint store and get a paint chip color chart. Then you go home, hold it up against the wall, and have a series of very earnest conversations about the relative merits of Milkweed versus Cornmeal versus Dove Gray versus Scone. Could you close your eyes and call to mind what any of these colors look like without having the paint chips in front of you? In the same way you can call to mind red or blue? Of course not. And I doubt that we’re in a Hilary Putnam-style reference borrowing situation: the people who work at the paint store don’t know the difference between Putty and Adobe Beige any better than you do. When you actually order a can of paint they’re going to make sure to write down the serial number.
So are paint chip terms words? From the discussion above, the answer seems like no. They have a little bit of semantics–a shade of red wouldn’t be called Moss–but they’re mostly just placeholders. It’s easier to say “I prefer the Fireweed” rather than “I prefer C5118” because the former is easier to remember and has fewer syllables. Once you’re dealing with more than four or so colors, though, it becomes easier to keep track of the serial numbers. I’m sure that’s what they use to take inventory at the paint store. But from a usage point of view, made-up color terms sure do act like words. People say and mean things like, “I like the Moody Blue better than the Blue Ox”. They get in fights with their spouses about them. These terms definitely refer.
Paint chip terms are a lexical corner case along along the temporal and speaker-count axes. How big is the language community that knows what Fawn means? It’s exactly as big as the number of people looking at the paint chip at that very moment. How long does that lexical item persist? Until you get the den painted.