Naming Factions, Guilds and Orders: Who Chose the Name?
Every group name in your story was chosen by somebody, and the single most useful question you can ask is which somebody. A name a group picked for itself and a name its enemies picked for it are different kinds of object, sound completely different, and carry opposite information. Most invented faction names never decide, which is why so many of them feel like logos rather than names.
Endonyms: what a group calls itself
Self-chosen names are aspirational, and they follow visible rules. They claim legitimacy, describe a mission, honour a founder, or simply mean "the people" in the group's own language, which is startlingly common among real ethnonyms.
They also tend to be dull, and this is the part fiction resists. Real organisations name themselves with committee language: the Society for the Protection of X, the Company of Merchant Adventurers, the Ministry of the Interior. A self-chosen name is usually a description of function wrapped in whatever formality the era favours, because it was drafted by the same kind of people who draft bylaws.
The craft implication is counterintuitive: a group's official name should often be blander than its reputation. The gap is the point. An organisation everyone fears that is formally called the Office of Standards is far more sinister than one called the Bloodhand Legion, because the blandness implies bureaucracy, and bureaucracy implies scale and permanence.
Where self-chosen names get vivid is in the smaller, younger, and more defiant group: the crew, the band, the street organisation. These names are advertisements. They claim territory, assert a reputation, or issue a warning, and they are short enough to shout. A gang name generator is working in exactly this register, and the same logic scales up to a mercenary company or a rebel cell.
Exonyms: what everyone else calls them
Names imposed from outside are the richer category and the more neglected. They are frequently insults, frequently mistakes, and frequently the name that survives.
An enormous number of real group names began as something the group would never have chosen. Some are descriptive of an outsider's first impression, keying on dress, weapon, or a distinctive practice. Some are a mishearing. Some are straightforwardly contemptuous, and several of history's more famous movements were named by their opponents and then adopted the insult deliberately, which is one of the most reliable moves in the whole repertoire.
That adoption is a gift to a writer. A group that has taken up a slur and wears it proudly tells you about its confidence, its humour, and its relationship to power, all in one word. And it lets you use a vivid, slightly absurd name without the artificiality of a group choosing something vivid and slightly absurd for itself.
Both names, at once
The strongest technique is to give an important faction two names and use both. The formal endonym appears in documents, treaties, and the mouths of its members. The exonym appears in dialogue, in the mouths of outsiders, and probably in your chapter titles.
Which name a given character uses instantly tells the reader where that character stands, with no explanation required. A character who switches from one to the other over the course of a story has visibly changed allegiance. This is one of the cheapest and most effective devices available, and it costs one extra name.
The four naming logics by group type
Guilds and trades name themselves for the work and the city, because their name is a legal instrument establishing a monopoly. Expect formality, expect a place name in it, and expect it to be long.
Religious and knightly orders name themselves for a founder, a saint, a virtue, or a relic, and the name is usually a phrase rather than a word: the Order of the Something of Somewhere. The shortened form used in speech is what your dialogue needs, so decide it. An order and the fortress it holds should share naming logic; a castle name generator and a kingdom name generator help keep the seat and the realm consistent with the order that serves them.
Military units are named by an administration, so they are numbered, and the memorable name is always the unofficial one the soldiers or their enemies coined. Both should exist in your text. The number is what appears in orders; the nickname is what appears in conversation.
Crews and companies name themselves after their ship, their leader, or their trade, and in maritime settings the ship's name usually wins, which makes the vessel's name load-bearing for the group.
Two failure modes
The first is the adjective-noun trap: Crimson Blade, Iron Covenant, Silver Dawn. These are not wrong, but they are so uniformly the default that a setting where every faction follows the pattern reads as a game menu. Break it by making some names a single word, some a phrase with a preposition, some a place, and some a person.
The second is names with no history. A faction three hundred years old should show wear: an outdated word in its formal title, a name referring to a purpose it no longer serves, an abbreviation nobody expands any more. Real institutions are full of these fossils, and their absence is what makes an invented organisation feel freshly minted for the plot.
The test
Say the name as a member would, with pride, and then as an enemy would, with contempt. If it only works one way, you have written half a name. Write the other half, decide which one the world uses more, and you will have a faction that feels like it existed before your protagonist heard of it.