Latin, machinator.

A machinator was probably a military engineer, responsible for the king's artillery. They are first recorded in Domesday Book, though given the importance of fortifications in England since the reign of Alfred the Great, siege engines and military engineers cannot have been introduced at the Conquest.

Only one engineer is recorded in Great Domesday, and he held no more than a couple of houses in Southampton (HAM S3), suggesting that machinators ranked rather lower in the technical and social scales than the Domesday

For more detail, see Jim Bradbury, The medieval siege (1992).