svarmi

One root, borrowed whole. There is no sv- prefix in Esperanto and no -armi suffix; svarm- is a single Germanic root that arrived intact, and the initial sv- cluster is a small clue that it did, because Esperanto's Latin layer almost never begins a word that way. Pronounce both consonants: "SVAR-mee", not "swarm-ee". Esperanto has no w sound and the v is a full English v.

Both the literal and the figurative sense are standard. Insects svarmi: bees leaving a hive, gnats over water, flies over anything. People svarmi when a crowd moves in all directions at once, which is a different picture from a queue or a march. And abstract things svarmi when there are simply a great many of them: demandoj svarmis en lia kapo, questions were swarming in his head. Esperanto uses the third reading more readily than English does, and it is a good word to have when you want to say "there were far too many of these" in one verb.

The noun, and a -ar- comparison. Svarmo is a swarm, and abelsvarmo is a swarm of bees. Notice that Esperanto has both svarmo and abelaro available here and they are not the same: abelaro is the colony considered as a unit, the bees as a collection, built with the collective -ar-. Abelsvarmo is the bees in flight, moving. So the difference is between a set and an event, and once you see it, amaso fits into the same picture: a heap or a crowd, standing still.

Around it. Svarmado is swarming as an ongoing activity. Ĉirkaŭsvarmi is to swarm around something, ensvarmi to swarm in. Svarmi je or svarmi de both mean to be teeming with: la merkato svarmis de homoj, the market was teeming with people, and the choice between je and de here is one of those places where usage has not fully settled and neither will be marked wrong. The tricky prepositions article explains why je exists at all.