Hebrew, A maul, and a sword, and a sharp arrow—a man that beareth false witness against his neighbour (see on Proverbs 25:11). One who bears false witness against his neighbour prepares for him the instruments of death, such as those mentioned here.
"A maul" (mephits), usually a heavy wooden hammer (compare malleus and "mallet"); here a club, or mace, used in battle, ῥόπαλον. There is a kind of climax in the three offensive weapons named—the club bruises, the sword inflicts wounds, the arrow pierces to the heart; and the three may represent the various baneful effects of false testimony, how it bruises reputation, spoils possessions, deprives of life.
The second clause is from the Decalogue (Exodus 20:16).