ἐπιορκήσεις, [1 verse](2nd sg aor subj act )"Thou shalt...forswear thyself," is epiorkeo, (2nd sg aor subj act) -- The Greek word translated as "forswear" specifically means "to swear falsely', "recant," or "renege" on a promise. Its meaning is literally "against an oath." Its root word is the same as the noun translated later in this verse as "oath."  It is the negative verbal form of that word below. This word is only used by Jesus here.which means "to swear falsely," and "to forswear oneself."