Solemnly
From BiblePortal Wikipedia
King James Dictionary [1]
Sol'Emnly, adv. With gravity and religious reverence. Let us solemnly address the throne of grace.
2. With official formalities and be due authority. This question of law has been solemnly decided in the highest court. 3. With formal state. 4. With formal gravity and stateliness, or with affected gravity. There in deaf murmurs solemnly are wise. 5. With religious seriousness as, I solemnly declare myselft innocent. I do solemnly assure the reader.
Webster's Dictionary [2]
(adv.) In a solemn manner; with gravity; seriously; formally.