When something is monolithic it's big, and made of one thing. A large piece of stone jutting from the earth is a monolith, and Detroit's economy when it depended entirely on the auto industry was monolithic.
Broken into its roots mono and lithic, monolithic means simply "one stone." When monolithic is used to describe something societal — like a religion or an organization — it has a slightly negative connotation. This is because anything made up of different people with different beliefs and goals is unlikely to be able to maintain monolithic status for long without force or oppression.
