Charles H. Spurgeon on Psalms 50:19

Thou givest thy mouth to evil, etc. Thou givest. Hebrew, thou sendest forth; to wit, free; for the word is used of men dismissing their wives or their servants, whom they left to their freedom. Thou hast an unbridled tongue, and castest off all restraints of God's law, and of thine own conscience, and givest thy tongue liberty to speak what you please, though it be offensive and dishonourable to God, and injurious to thy neighbour, or to thy own soul; which is justly produced as an evidence of their hypocrisy. To evil, either to sinful or mischievous speeches. Frameth deceit, i.e., uttereth lies or fair words, wherewith to circumvent those who deal with them. Matthew Poole.