What is an antonym for dissertation?

There isn't a single perfect antonym for "dissertation" because it describes a specific thing. However, depending on the context, you could use words that represent the opposite *idea* of a dissertation:

* Summary: If you're contrasting the length and depth, a summary is the opposite.

* Outline: If you're contrasting the completeness, an outline is the opposite.

* Abstract: This is a shorter version, but not quite an antonym.

* Trivial note: This highlights the contrast in significance and length.

The best antonym will depend heavily on the context in which you're using the word.