The Greek term is \""sabbaton\"" G4521 - which means literally \""seventh day of the week\"".
However, they are incorrect, because they do not understand that Pharisees had a common saying that refered to a law of fasting twice a year, in their law.
The Pharisee in his prayer did not say \""I fast twice a week\"", but rather was refering to a strict custom commonly known among the Pharisees, which is called the \""two sabbath a year fast\"":
