Albert Barnes Commentary Psalms 109:2

"For the mouth of the wicked and the mouth of deceit have they opened against me: They have spoken unto me with a lying tongue." — Psalms 109:2 (ASV)

For the mouth of the wicked and the mouth of the deceitful - literally, “The mouth of wickedness, and the mouth of deceit.” This informs us about the nature of the wrong that had been done to him. It was slander; undeserved reproach.

Are opened against me - Margin, “have opened;” that is, they have opened themselves.

They have spoken against me with a lying tongue - They have accused me of things that are not true; they have made false charges against me. David, as has not been uncommon with good people, was called repeatedly to this trial.