Klaus Baudelaire is a rather intelligent child. Despite his age, 12 years old, he has a rather impressive lexicon. "Lexicon" is a word which here means: "The vocabulary of a person"
The word, "Vocabulary" is a word which here means: "The body of words known to an individual person", and since the two words' definitions are so similar, the two words' are synonymous. The word "Synonymous" here means: "Having the same or nearly the same meaning as another word or phrase of the same language."

What I have just written is a very long and complicated series of descriptions that might have bored some of the simpler minds reading this, but it is a very long and complicated series of descriptions that a boy such as Klaus Baudelaire.
Klaus Baudelaire is a main character and as such will have a great many lines