What is the correct spelling of an official promise?

The correct spelling of the word for an official promise is Oath: o-a-t-h, four letters, with the vowels o-a together and the consonant cluster -th at the end. The word comes from the Old English ath, of Germanic origin and cognate with the Old Norse eithr and the Old High German eid. There are no common spelling errors for the basic four-letter form, although applicants may second-guess the silent th cluster or add an extra letter (Oathe).

On the USCIS writing test sentences containing oath are common, including "Citizens take the oath of allegiance," "What oath do new citizens take?" and "The President takes an oath."

In U.S. legal practice an oath is a solemn declaration that something is true or that the speaker promises to do something, often invoking a higher power but always carrying legal force. False statements made under oath constitute the federal crime of perjury under 18 U.S.C. section 1621.

Several oaths shape U.S. civic life: the presidential oath of office (Article II, section 1, clause 8 of the Constitution), the oath taken by members of Congress and federal officials (5 U.S.C. section 3331), the oath witnesses take in court (Federal Rule of Evidence 603), and the Oath of Allegiance taken by new citizens at the naturalization ceremony (8 CFR section 337.1). Applicants whose religion forbids swearing may affirm rather than swear, with no change in legal effect, under the constitutional provisions in Article II and Article VI. The word also appears in many official contexts beyond naturalization, including grand jury testimony, federal employment forms, and the swearing-in of military officers and federal judges.