an open book

Translations
открытая книга
She is an open book when it comes to her emotions.
Она — открытая книга, когда дело касается её эмоций.
Definitions
A person whose thoughts, feelings, and motivations are easily understood or who is very transparent and honest in their behavior and communication.
Words
an

article or possessive pronoun
неопределённый артикль
open

adjective
открытый
book

noun
книга