Xenonominal
An individual is someone whose name falls outside the typical understanding of names. These individuals will usually have an identity which also isn't typically human.
For example;
the name is a certain sound or song
the name is a feeling or sensation
the name is a specific sight or image
the name is nonhuman in nature e.g. alien headmate having a name in its language
the name is not pronounceable by humans
They may use a name in human spoken language because it is socially expected and easier to use.
Xenonominal people can have varying degrees of identification with that chosen name. It could be:
the closest approximation to their actual name
something related to the contents of their actual name
a name they find aesthetically pleasing
a name sourced from media
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This term is free to use for humans, nonhumans, and all types of headmates/system members. I coined this for personal use as a system member - my true name can only be communicated internally, outside I just go by J.