Shorts

There is a class of word that, while it describes other things, includes itself in that description, thus both defining a meaning, and demonstrating it in a short space

sesquipedalian

is an example. It refers to very long words (lit. a-foot-and-a-half-long) and is itself at 14 letters trying to stretch into the forever, something that its synonym

inkhorn word

at 11 letters (if you include the full term) doesn't match. Similarly,

broaden

counts, because it is broader than broad, though

thinner

is no skinnier than its progenitor. My own small contributions to this list:

glo'al stop

replacing the [tt] with itself, and (my favourite)

innuendo