Cast
A cast was a weapon created by the Great Houses.
Insubstantial and mindless, they were hardwired into the Homeworld's noosphere or the operating system of a timeship. When activated, the cast absorbed radiation from the vicinity and changed it into baryonic matter (giving solidity) or strange matter (enabling it to exist in two, one or zero dimensions, essentially making them invisible).
A more advanced version, the babels, were created long before the War. They were abandoned after they were found to be insane, with an escaped one committing mass murder at House Catherion.
The casts were used in the War, but were effectively useless, especially against the conceptual entities which they somewhat resembled. (PROSE: The Book of the War)