Tmolus was a god or a king associated with Mount Tmolus who decided the musical contest between Apollo and Pan. According to some accounts he was the husband of Pluto (the daughter of Cronos) and the father of Tantalus.
His name is almost certainly not Greek in origin, and the only Greek word remotely resembling his name is tmego, 'to cut', 'be divided'. This is so general that it could apply in a number of ways according to whim: for example the musical contest could be said to be 'cut' or 'divided' by Tmolus.