Alicornutopia

An entire name, even if it is too short to count as part of a longer name, always counts.

Ooh, that gives me a great idea: initially-name babies with sounds that draw from sources other than the actual phonemes of your native language. Like, I just totally pronounced the name [sharp exhale between teeth][chirp] out loud, it has things resembling consonants and vowels in it, but you could stand around all day guessing every conceivable combination of valid English noises and not come up with it. Harder to write it down and keep a copy, admittedly.

Regarding entire names: so if you name someone, say, Iuuaiaeie, which has no consonants, will any subsequence of multiple vowels count or would someone have to come up with the whole string correctly?

Any sequence of multiple vowels will count.

What about a culture that doesn't primarily use spoken language?
Would a sign language name let a faerie control you?

Also, the Bartimeaus universe could be interesting here.
Magicians are not told their birth names, since it would give demons power over them.

If the fairy learns the name, it still counts - if Celo tells his name to a fairy he's got, the fairy just can't pronounce it. Similar for name signs except the fairy *can* pronounce it.

Can't pronounce is a partial defense, in that they can't then share your name?

If you manage to give someone a name that literally harms someone to hear it, would that mean that someone literally couldn't give a master who had food-trapped them or whatnot their name?

Ooh. Nice one, Maggie. I can even think of some notions that might potentially qualify.

(Why am I awake at this hour? We just don't know.)

They can't directly share your name; they can make you say it, if you can pronounce it.

Maggie: that is super smart and would totally work as far as it goes. If your name is from that one Monty Python sketch or something, your food!master will have to make you tell a third party and the third party will have to tell your master if they don't want to go without altogether.

What if someone has a name that they themselves can't pronounce? Like the nymph deal but without the convenient ability to share it? I guess in a nymph's case the sensory impression is usually theoretically achievable by standing around in their field waiting for the right meteorological conditions...