Jess A
Archmage
A merchant association might be called a compagnie (French) or a Hansa or Zuenft (German). In English, company will do fine. You should think of the word more like a company of mercenaries -- a group of people come together for a specific purpose. Mercantile companies were not at all like a modern corporation; they were a true association of participants, with the members buying shares of the overall enterprise. They were often formed to buy into a ship or even a fleet of ships. The company would exist for the duration of the voyage, then would split the profits (or losses) and then dissolve. On land, families tended to be the basis for commercial enterprises. See the Medici in Florence, the Fuggers or Welsers in Augsburg, the Paumgartners in Nuremberg, for examples.
The term "merchant adventurer" doesn't crop up until late 16thc ("adventure" here is in the sense of a venture). The term brotherhood was used as well, but that's more medieval and might confuse readers.
Definitely not a union.
Points taken. I had a book on the Medici somewhere. I need to dig it up. Also, Robin Hobb did a portrayal of merchants/traders (Liveship Traders) but it has been a long time since I read them. It'll be a big research point for me, because I like to work with detail and then change it to suit my world. Thanks again!