a solemn pledge

Translations
торжественное обещание
He gave a solemn pledge to uphold the law.
Он дал торжественное обещание соблюдать закон.
Definitions
A solemn pledge is a serious and formal promise or commitment made by an individual or group, often with a sense of gravity and sincerity, to uphold certain principles, duties, or actions.
Words
a

article or possessive pronoun
неопределённый артикль
solemn

adjective
торжественный
pledge

noun
обещание