Hornbook and Intro

Hornbook noun - A primer that provides instruction in the rudiments or basic skills of a branch of knowledge.

Intro and hornbook are semantically related in something new topic. In some cases you can use "Intro" instead a noun "Hornbook".

Intro noun - A short section (as of a book) that leads to or explains the main part.

Hornbook and intro are semantically related in something new topic. Sometimes you can use "Hornbook" instead a noun "Intro".