let (someone) down

Translations
подводить (кого-то)
I promised to help, so I can't let her down.
Я обещал помочь, так что я не могу её подвести.
Definitions
To disappoint someone by failing to do what was expected or promised, or by not providing the help or support they needed.
Words
let

verb
позволять
down

adverb
вниз