A phrase like 'under a vow' is not a part of speech. It is a phrase that is made up of parts of speech.
under is a preposition
a is an article
vow is a noun
"Vowed" is the past tense of the verb "vow," which means to make a solemn promise or commitment. It is a verb.
No, the pope is not under a vow of silence.
Snape agreed to make a magical vow called the unbreakable vow. He swore to protect Draco Malfoy.
The term "altar vow" is not used in the Catholic Church, the only reference that I can find to it is a quote in a novel from a long time ago where "altar vow" is used to refer to the marriage vows that a man and a woman make before the altar.
Ellen - 1994 When the Vow Breaks Part 1 3-24 is rated/received certificates of: USA:TV-PG
Ellen - 1994 When the Vow Breaks Part 2 3-26 is rated/received certificates of: USA:TV-PG
Ellen - 1994 When the Vow Breaks Part 1 3-24 was released on: USA: 8 May 1996
He said he'd only serve for one term, which in fact he did.
Letter to Loretta - 1953 The Eternal Vow Part 1 7-28 was released on: USA: 15 May 1960
Letter to Loretta - 1953 The Eternal Vow Part 2 7-29 was released on: USA: 22 May 1960
no they did not that is just part of rick reodions story.
A vow of celibacy.