Names in general
"I didn't think to name it." Cas glances at Dean's arm as he pushes up the sleeve. "Do humans have particular naming conventions I should be aware of?"
Chuck's head snaps around. "How did anyone know to use it without a name? I mean, do angels just--" he trickles off, like he's not sure how to finish that sentence. "Know it?"
"No, of course not. Everything was given a name when time began."
[...]"This didn't exist then," Cas continues. "Hence, it did not receive a name [...]"— Map of the World, ch. 3, regarding Cas's sigils
"Right, I need her name. What is it?"
"She doesn't have one."
"You're fucking with me."
"No, I'm not," Lia answers distractedly, staring at the door with an expression he can't read. "You can't call her without one, and she'll only answer to one she recognizes as her own."— Dean and Cornelia Africana in Map of the World, ch. 11
"My true name is Cornelia, Dean."
Dean doesn't sigh, but it's hard. "Nice to meet you, Cornelia. Now can we--"
"You know my true name because I gave it freely," she says, holding his eyes, and he wonders if it's just him or if she's getting brighter.— Map of the World, ch. 11
Names have power, he's always known that, but the most powerful is the one that you use to define yourself. There's a reason Rumpelstilskin was required reading when [Dean] was a kid, with added Dad-administered quiz.— It's the Stars That Lie, ch. 7
Dean winces. Cas is just lucky he doesn't have a middle and last name to drag out and throw at him; that tone just begs for it.— Map of the World, ch. 2
"Qafsiel Kaziel, Cassiel, Messenger, by whatever name, with whatever rite, in whatever appearance it is right to invoke thee, I entreat you to grant me a single request."
"Castiel." Gaius's eyes widen at the offered name. "My true name is Castiel."— Map of the World, ch. 11
"Cas…." Dean tries to think how to put this. "When you started hunting, did Dean--I mean, you were here full time and everything. He ever--you know, get you a name?"
"I had many aliases--"
"Not for jobs, just--I don't know."— It's the Stars That Lie, ch. 4
Cas had a dozen aliases on earth before he even got his own name; it makes sense that he became a hunter before he learned the first principles of being human.—
I'm not an angel anymore, nor do I have Grace, so my true name has very little practical power over me, but it's still my name, and its existence gives it power.— Castiel in It's the Stars That Lie, ch. 7
Dean scrawls his (honestly, terrible) signature at the bottom before turning it and sliding it across the table to Cas, offering the pen when Cas looks at it in bewilderment. "What?"
Cas looks baffled, but at least he takes the pen. "Why?"
"Because it's your job," he answers patiently and it's only with an effort he manages not to laugh at Cas's expression. "Officially. So put your name on the nice piece of paper below mine."
Cas looks between Dean and the pen before focusing on the paper in front of him again. Biting his lip, he hesitates before signing just below Dean in his ridiculously flawless script. Swallowing hard, Dean reads the name: Castiel Singer, Chitaqua.
He chews his lip. "Is that--"
"Yeah," Dean answers, clearing his throat hastily. "This is exactly what you use it for."— A Thousand Lights in Space, ch. 2
"What about the prayers to 'you fucker'?"
"I explained in detail the myriad dangers of an angel choosing to formally acknowledge anyone addressing them with a name not their own," he answers solemnly, blue eyes wide and guileless. "I offered to compile a list of my acknowledged names for his perusal, but he assured me that 'Cas' was adequate."— Dean and Cas about Endverse!Dean in A Thousand Lights in Space, ch. 4
- To the world outside Chitaqua/Ichabod, Cas is known as "Jimmy Novak, alias Castiel," and assumed to be guilty of various serious crimes.
- Bobby picked the name Castiel Gabriel Singer to procure (presumably non-fake) IDs for Cas. Cas says about it: "I suppose if someone asked me for my full name, that's what I would tell them."
- As an angel, Cas went by various different names: Qafsiel Kaziel, Cassiel, Messenger (and, of course, Castiel).
- Dean knows what the true sigil form of Cas's name looks like by heart, and Cas gave that information freely to him. In using this sigil for warding Chitaqua, Cas contamines the binding.
- Several times over the past two years, the angels that rule in Hell have tried to unmake Cas's name. But it never takes, and every time it fails faster than the time before. 
He's still invisible, though, behind a name even more powerful than Cas's sigils, because now they look right at him and talk to him and take his orders and still don't see him at all.— Dean reflecting on his disguise as his Endverse counterpart in Map of the World, ch. 4
- Dean's name is known internationally, as he is assumed to be guilty of various serious crimes.
- A recurring phrase used by Cas is 'in Dean's name' (or a variation thereof):
- "Give me a week and your team leaders, and I'll bring Kansas to its knees in your name."
- "[F]or you, hundreds of my Brothers died trying to free you from Hell, and it was in your name I took the lives of those who survived, in nomine Dean--"
- Regarding the sigils: "All things must have a name, Chuck was right, and it did; I named it after you."
- Angels can be summoned by using their true names.
- According to Cas, an angel could use their "public name, usually a translation of their true name from Enochian" to mark a human as their own.
- Castiel says about angels: "Their true name, willingly given and willingly accepted, would be binding to them as well. No angel would give a human equal power over them." He has freely given his true name to Dean.
- Like Castiel, Anna also used to go by a variety of names: Anina, Namina, Anael, Ana-el, Messenger.
Residents of Chitaqua and Ichabod
"We don't use [last names] here."
"Some of us are using aliases because of our multiple federal warrants or hiding our last names because of same," Dean answers, thinking fondly about how impressively wanted his militia is, and under way more names than he thinks anyone should have to keep straight, which come to think…. "It's not just that."
"The military are the only ones who offered surnames, and for the reasons you mentioned, we tended not to," Cas answers meditatively. "However, even with our limited contact with other residents of the state before now, I don't remember surnames being offered to patrol, and at least for them, there was no reason to conceal them. Here--I suppose it's unnecessary, as we all know each other [...] Surnames in their various forms were historically used for the purpose of tracing lineage, claiming membership in a clan, tribe, or extended family group, identify their origin, or in some cases, as a more specific form of identification in very large groups [...] They also acted as a means of separating individuals into identifiable groups. In smaller populations, however, it's not common for them to be used for reasons other than ceremonial."— It's the Stars That Lie, ch. 4
"So you just pulled 'Ichabod' out of thin air?" Dean asks Alison dubiously [...] "What was the name of the town before, anyway?"
Alison gives him a patient look not unmixed with disappointment, followed by resignation that he's what she's got, so she's making the best of him. He gets from her a lot.
"It was abandoned," she answers.— A Thousand Lights in Space, ch. 1
"A bottle of Eldritch Horror," [Dean] answers, adding in bewilderment, "I have no idea how that name has spread so quickly or how it became so popular."— It's the Stars That Lie, ch. 8
"You got a name for your laptop?" Dean asks, deliberately bracing a foot on the dashboard and biting down the smile of bitter satisfaction at Cas's there-and-gone frown.
"Yes, but as you know, knowing the true name of anything gives you power over it," Cas answers, flickering another glance at Dean's boot. "Why?"
"I'm calling it 'thing I covered in salt and set on fire in the front yard'," Dean answers venomously. "I like it; what do you think?"— A Thousand Lights in Space, ch. 4
- Map of the World, ch. 2
- It's the Stars That Lie, ch. 4
- Map of the World, ch. 11
- It's the Stars That Lie, ch. 7
- The Game of God, ch. 8
- It's the Stars That Lie, ch. 8
- A Thousand Lights in Space, ch. 6