The phrase "rich vocabulary" means having a wide variety of words and phrases that a person knows and can use when speaking or writing. Full definition
You can find curated collections of texts that use rich vocabulary at Steps to Literacy. (educationworld.com)
They include rich vocabulary, age - appropriate text, a variety of art styles and media, and a clear connection to at least one theme per book. (appletreeinstitute.org)
The story is bilingual, so it provides rich vocabulary - building opportunities. (readingbrightstart.org)