I'm reading Neal Stephenson's historical novel Quicksilver, published in 1998 and set around 1700. There are several passages where the characters use the word ninehammer, as in the following:
"... For never have you seen such a gaggle of frauds, fops, ninehammers, and mountebanks."
(Book Three, "Daniel and Churchill on Tower Causeway". This scene takes place in London in 1688, and the character speaking, Daniel Waterhouse, is an English gentleman.)
It seems that this is meant to be a variant spelling of the archaic word ninnyhammer, meaning roughly fool, which is apparently the origin of our modern word ninny. But I wasn't able to find any other sources using this spelling.
Is there any evidence that this spelling was ever in common use, or is it an invention of the author?
The word appears several times in the novel, consistently spelled ninehammer, so it seems unlikely to be a typographical error.
I did find a post on Wordwizard that investigates this word and discusses the etymology of ninnyhammer, but it also doesn't seem to find any evidence that the spelling ninehammer is historical.
It should be noted that the dialogue in the novel is sometimes clearly anachronistic, which is evidently a conscious choice by the author.