I could not find any references to ‘naysmith’ as an actual historical term.  Following is an excerpt from the book ‘Horus Rising.”

> ‘Then it occurs to me, Garviel, that only a weapon which questions its use could be of any value in that role. To be a member of the Mournival, you need to have concerns. You need to have wit, and most certainly you need to have doubts. Do you know what a naysmith is?’

> ‘No.’

> ‘In early Terran history, during the dominance of the Sumaturan dynasts, naysmiths were employed by the ruling classes. Their job was to disagree. To question everything. To consider any argument or policy and find fault with it, or articulate the counter position. They were highly valued.’

\- Horus Rising, pg. 68