Who whet their tongue like a sword - Who sharpen their tongue; that is, they utter words that will cut deep, or penetrate the soul. The idea is that of slander or reproach - the same idea which we have in Shakespeare (Cymbeline):
“‘Tis slander;
Whose edge is sharper than the sword.”
This comparison is a favorite one with David. Compare Psalms 52:2; Psalms 57:4; Psalms 59:7.
And bend their bows ... - That is, they prepare for this - as they make ready to shoot who bend their bows, and fix their arrows on the string. The idea here is, that this was deliberate, or was the result of counsel and purpose. It was not an outbreak of mere passion and excitement; it was by fixed design and careful preparation. See Psalms 11:2, note; Psalms 58:7, note.
Even bitter words - We apply the same term bitter now to words of malice and reproach.