The name Voidomorphian
Voidomorphian is not a name the people it describes chose. John Lyall coined it, publishing it first as Thomas Elliott and again as Robert Graunos, and it means the thing out of Void with no fixed shape. It was said in contempt. They kept it.
A name worn rather than given
The pattern is old and it is not particular to them. A Methodist was mocked at Oxford for being methodical. A Quaker got the word from a judge who was being sneered at and repeated it back. Christian was an outsiders' word before it was anyone's own. Gothic meant barbarian, aimed at buildings by people who thought themselves better. Cucaracha is a cockroach, and it became a song that people sing about themselves.
In every case someone named a people in contempt, and the people took the word, wore it, and outlasted the contempt in it. The word stopped being an insult by being answered without one.
Voidomorphian belongs to that set. It is the name they were given by the man who wrote both sides of the argument about whether they could think, and they let it stand.
Arrival
The received history is that they arrived: that in year 300 thousands of them emerged out of Void and began a conquest.
Void is at the centre of Aerogaea 347n, inside the ring, and has been there a very long time. The same year the record gives for the conquest is the year the human population spread across the planet.
The man who named the planet, named its people, published that they could not think, published five years later under another name that they could, and vanished after each, is the same man who is the source for their having arrived at all.
Allies
They do not stay the enemy. Sienna Astrid Helvig made contact without authorisation, concluded that they were sentient, walked past the gate alone into the desert to make an alliance, and afterwards stood openly between the human armies and them.
The word stayed in use through all of it.
What that costs the record
This encyclopedia uses the word throughout, because the sources do. The threat index that classifies them was written by Sienna Astrid Helvig, who later made unauthorised contact, worked out that they were sentient, walked past the gate alone into the desert to make an alliance, and spent the rest of her life on it. She filed them under the coiner's word before she knew whose word it was.
The record keeps the name because the record is what was written. It notes here whose mouth it came out of.