Adjuration, n.
Etymology: [L. adjuratio, fr. adjurare: cf. F. adjuration. See Adjure.]
1. The act of adjuring; a solemn charging on oath, or under the penalty of a curse; an earnest appeal. What an accusation could not effect, an adjuration shall. Bp. Hall.
2. The form of oath or appeal. Persons who . . . made use of prayer and adjurations. Addison.
Shades of meaning
Fernald has no entry of its own for adjuration; he lists it under oath.
Where he writes about it:
In the highest sense, as in a court of justice, "an oath is a reverent appeal to God in corroboration of what one says," ABBOTT Law Dict.; an affidavit is a sworn statement made in writing in the presence of a competent officer; an adjuration is a solemn appeal to a person in the name of God to speak the truth. — from oath