But he began to curse and to swear, [saying], I know not this man of whom ye speak.
Note 5 at Mr 14:71: Matthew and Mark used two different Greek words for this cursing that Peter did. Both of these Greek words are describing the action of binding oneself with a curse rather than a use of profanity. Both Greek words (in Mt 26:74 - "KATANATHEMATIZO" and in Mr 14:71 - "ANATHEMATIZO") are derivatives of the Greek word "ANATHEMA" that is used in 1Co 16:22. In that case, it clearly speaks of being accursed.