Shyster

 

I just looked it up in the Oxford English Dictionary, which is probably the ultimate arbiter on words.

It describes shyster as "(colloquial) person without professional honour, especially a tricky lawyer". The origin is given as 19th century and as uncertain.

As someone who is married to a lawyer, who knows about libel, it would appear that it would be easy to defend calling someone a shyster in a court of law, if you had the evidence.