Then king Solomon sware by the LORD, saying, God do so to me, and more also, if Adonijah have not spoken this word against his own life.

Then king Solomon swore by the Lord, saying: So and so may God do to me, and add more, if Adonias hath not spoken this word against his own life.

And king Solomon sweareth by Jehovah, saying, 'Thus doth God to me, and thus He doth add, surely against his soul hath Adonijah spoken this word;

Then King Solomon took an oath by the Lord, saying, May God's punishment be on me if Adonijah does not give payment for these words with his life.

And so king Solomon swore by the Lord, saying: "May God do these things to me, and may he add these other things! For Adonijah has spoken this word against his own life.

Against his own life - Adonijah had forfeited his life by his former conduct, and his pardon had been merely conditional 1-Kings 1:52.

Then King Solomon sware by the Lord,.... To prevent his mother pressing him to have her petition granted:
saying, God do so to me, and more also; lay such and such evils upon me, and more than I care to express:
if Adonijah have not spoken this word against his own life; to his own prejudice, and even to the loss of his life; in which Solomon suggests it would issue, being a fresh overt act of treason; he knew, from what Bathsheba said, that this was his petition, and that he had spoken of this to her, and put her upon making it for him; and who no doubt related to Solomon the whole of the conversation that passed between them, and to which he seems to have some respect in his answer.

God do so to me, and more also--the common form of introducing a solemn oath.
if Adonijah have not spoken this word against his own life--Whether there was a treasonable design to conceal under this request or not, the act, according to Eastern notions, was criminal, and of dangerous consequence to the state. There is no ground of censure upon Solomon for cruelty or precipitation in this instance. He had pardoned Adonijah's former conspiracy; but this new attempt was rebellion against the viceroy appointed by the divine King and called for condign punishment. The office of executioner was among the Hebrews, as in other ancient countries of the East, performed unceremoniously and privately--often without any previous warning--by the captain of the guard, or one of his officers (Matthew 14:10).