Definition from Wiktionary, the free dictionary
sophist (plural sophists)
- One of a class of teachers of rhetoric, philosophy, and politics in ancient Greece.
- A teacher who used plausible but fallacious reasoning.
- (by extension) One who is captious, fallacious, or deceptive in argument.
Usage notes 
- The meaning of "sophist" can vary depending on the time period to which one is referring. A sophist of the earliest period was a master in his art or craft who demonstrated (taught by example) his practical skill/learning in exchange for pay. Later sophists were providers of a well-rounded education intended to give pupils arete – "virtue, human excellence". By late antiquity, sophistḗs / sophistes tended to denote exclusively a skilled public speaker and/or teacher of rhetoric.
- (one who is captious, fallacious, or deceptive in argument): logic chopper
Related terms 
ancient teacher of rhetoric, etc.
one who is captious, fallacious, or deceptive in argument