His mouth is full of cursing and deceit and fraud: under his tongue is mischief and vanity.

His mouth is full of cursing, and of bitterness, and of deceit: under his tongue are labour and sorrow.

Of oaths his mouth is full, And deceits, and fraud: Under his tongue is perverseness and iniquity,

His mouth is full of cursing and deceit and false words: under his tongue are evil purposes and dark thoughts.

His mouth is full of cursing and bitterness and oppression. Under his tongue is mischief and iniquity.

His mouth is full of cursing. The scope of these four verses is this: If God intends to succor his servants, it is now a proper time for doing so, inasmuch as the lawlessness of the ungodly has burst forth to the utmost possible excess. In the first place, he complains that their tongues are full of perjuries and deceits, and that they carry or hide mischief and wrongs, it being impossible to have any dealings with them in any matter without loss and damage. The word 'lh, alah, which some render cursing, does not signify the execrations which they throw out against others, but rather those which they call down upon their own heads: for they do not scruple to utter the most awful imprecations against themselves, that thereby they may the better succeed in deceiving others. It is, therefore, not improperly rendered by some, perjury, for this word ought to be joined to the other two, deceit and malice. Thus the wicked are described as cursing or swearing falsely, so far as it contributes to forward their purposes of deceiving and doing injury. Hence follow mischief and injustice, because it is impossible for the simple, without suffering detriment, to escape their snares, which are woven of deceits, perjuries, and malice.

His mouth is full of cursing - Profaneness; blasphemy against God. In the former verse the writer had described the feelings of the "heart;" he now proceeds to specify the open acts of the wicked. The meaning is, that the wicked man, as here described, was one who was full of imprecation, swearing, execration; a "profane" man; a man who, whatever was his belief about God, would constantly call upon his name, and imprecate his wrath on himself or others. An atheist, strange as it may seem, is as likely to make a frequent use of the name of God, and to call upon Him, as other people; just as profane people, who have no belief in the Saviour, swear by Jesus Christ. This passage seems to be referred to by the apostle Paul in Romans 3:14, not as a direct quotation, as if the psalmist referred to the point which he was arguing, but as language which expressed the idea that the apostle wished to convey. See the note at that passage.
And deceit - Margin, as in Hebrew, "deceits." The meaning is, that he was false and treacherous; and perhaps also that his treachery and fraud were accompanied with the solemn sanction of an oath, or an appeal to God, as is likely to be the case among fraudulent and dishonest people.
And fraud - The word used here - תך tôk - is now commonly supposed to mean rather "oppression or violence." See Gesenius' Lexicon. When this is attributed to his mouth, it means that what he says - what he requires - what he commands, is unjust, unreasonable, and oppressive.
Under his tongue - Perhaps alluding to the serpent, whose poison is concealed at the root of the fang or tooth, and therefore under the tongue. The meaning is, that beneath what the wicked say, though it seems to be harmless, as the tongue of the serpent does, yet there lies mischief and iniquity, as the poison is hidden beneath the serpent's tongue.
Is mischief - The word used here means properly labor, toil; then trouble, vexation, sorrow. The meaning here seems to be that there lies under the tongue that which gives or causes distress; to wit, wrong-doing; injustice to others.
And vanity - Margin, iniquity. This expresses the idea in the original word. Whatever he says is evil, and is fitted to produce trouble and sorrow, as the concealed poison in the mouth of the serpent causes pain and death.

His mouth is full of cursing, and deceit, and fraud - What a finished character! A blasphemer, a deceitful man, and a knave!

His mouth is full of cursing,.... Or, "he has filled his mouth with cursing" (e) God and good men, his superiors, himself and others. The word signifies "an oath"; and may design either a profane oath, taking the name of God in vain; or an oath on a civil account, a false oath, taken with a design to defraud and deceive others, as follows, and intends perjury; and this, as applicable to antichrist, regards his mouth speaking great things and blasphemies against God, and uttering curses and anathemas against the saints, Revelation 13:5;
and deceit and fraud; such as flattery and lying, which are both used by him with an intention to impose upon and deceive. The apostle, in Romans 3:14; renders both these words by one, "bitterness"; which may be said of sin in general, which is a very bitter thing; though it is rolled as a sweet morsel in the mouth of a wicked man, yet in the issue it is bitterness to him: and it is applicable to sinful words, which are bitter in their effects to those against whom they are spoken, or who are deceived and imposed upon by them: and, as they refer to antichrist, may have respect to the lies in hypocrisy spoken by him, and to the deceitfulness of unrighteousness, by which he works upon those that perish, 1-Timothy 4:2;
under his tongue is mischief and vanity; alluding to serpents, who have little bags of poison under their teeth; see Psalm 140:3; Kimchi and Ben Melech observe, that the heart is under the tongue, being lower than it, and so denotes the wickedness which that is full of, and devises continually, and is latent in it until discovered; and is mischievous iniquity, injurious to God, and the honour of his law, and to fellow creatures; and especially to the saints, whose persons, characters, and estates, are aimed at; but in the issue it is all vanity, and a fruitless attempt, being blasted by God, and overruled for good to him; see Isaiah 54:17;
(e) .

The malignity and deceit (Psalm 140:3) of such are followed by acts combining cunning, fraud, and violence (compare Proverbs 1:11, Proverbs 1:18), aptly illustrated by the habits of the lion, and of hunters taking their prey. "Poor," in Psalm 10:8, Psalm 10:10, Psalm 10:14, represents a word peculiar to this Psalm, meaning the sad or sorrowful; in Psalm 10:9, as usual, it means the pious or meek sufferer.

Tongue - Under his fair and plausible speeches, mischief is hid and covered. Vanity - Or, injury, the vexation or oppression of other men.