Astromarine
Erudite
My idea would be something veiled that euphemizes their trade. In fact, if you didn't go with the Commercium for the Merchant's guild, I would suggest that for your *assassins* guild. Just like, for example, in Discworld the Guild of Seamstresses doesn't *exactly* sow.
The idea would be that they view themselves as just that, merchants. Too bad your backstory is already written, it would be neat to even have them be a logical offshoot of the merchant guild. Still, if your idea is to have them possess a veneer of "honorable businessmen" it would make sense for them to have such an innocuous name to outsiders. It would make more sense to them than trying to sound "badass and mysterious". You know, just like those organizations in bad spy movies: "the Firm", "the Section", "Control", etc. In that case, it would "The Commercium", the traders. Exactly *what* they trade, you can wish you'll never have to find out.
etc.
The idea would be that they view themselves as just that, merchants. Too bad your backstory is already written, it would be neat to even have them be a logical offshoot of the merchant guild. Still, if your idea is to have them possess a veneer of "honorable businessmen" it would make sense for them to have such an innocuous name to outsiders. It would make more sense to them than trying to sound "badass and mysterious". You know, just like those organizations in bad spy movies: "the Firm", "the Section", "Control", etc. In that case, it would "The Commercium", the traders. Exactly *what* they trade, you can wish you'll never have to find out.
etc.