What is an antonym for chapter?

There isn't a single perfect antonym for "chapter" because its meaning depends on the context. Here are some possibilities, depending on the intended meaning:

For "a section of a book":

* Whole: This implies the entirety of the book rather than a single part.

* Part: This is the opposite in a general sense, but it's less specific than "chapter."

For "a period of time in someone's life":

* Moment: This refers to a very brief period of time.

* Phase: This implies a more extended period of time, but it's less specific than "chapter."

For "a branch of an organization":

* Whole organization: This implies the entire organization rather than a specific part.

* Department: This is a more specific synonym for "branch," but it doesn't have a clear antonym.

The best antonym for "chapter" will depend on the specific context in which it is used.