Gremio (Spanish for “union,”, in the sense of workers, unite!; formerly “guild”–which is really just an old-school union!) comes from the Latin Gremium, meaning “round.” How did this transformation happen? Well, a round pen was where you held onto things; it turned into the word for where people got together, which turned into guild (a common reason people got together!) and then, eventually, to mean union.
However, it gets much more interesting. The Latin gremium comes from the proto-indo-european root *ger- meaning.… to get together! From this root, we also get (via Greek) words like congregate (to bring people together) and segregate (to bring people apart!).
Thus, gremio took an interesting turn over the last few thousand years: from the meaning congregate to round to congregate again!
We can see the g‑r root clearly in gremio as well as congregate and segregate.