What is a synonym for the word gargantuan?

Here are some synonyms for "gargantuan", depending on the context:

Formal:

* Colossal

* Enormous

* Gigantic

* Immense

* Monumental

* Vast

Informal:

* Huge

* Massive

* Tremendous

* Whopping

* Ginormous (slang)

The best synonym will depend on the specific context and tone of your writing.