It's fair to say that some monoliths could count as monuments, but it's stretching it to say that it is a synonym.
Block, column, monument, pillar and statue are all synonyms for the word monolith.
monolith
A monolith refers to a large, single, and typically impressive structure or monument. In the context of technology, a monolith can also describe a software architecture where the entire application is structured as a single unit.
An antonym is an "opposite name" such as small and big are antonyms. A synonym is a "together name" such as small and little are synonyms. An obelisk is a 4-sided stone pillar. Synonyms include column, monolith, monument, pillar, pylon, tower. There are no listed antonyms for the word obelisk.
The root word "litho" in "monolith" originates from the Greek word "lithos," which means "stone." Therefore, "monolith" literally means "single stone," reflecting the idea of a large, single upright stone monument or structure.
Mt Augustus (Burringurrah, as it is known by Wajarri Yamatji aboriginals. It is significantly larger than Uburru, also in Australia. This monolith is also called Ayers Rock by the white population.
an obelisk, column, large statue, etc., formed of a single block of stone
Gravestone inscription.
Monolith Soft's population is 2,012.
Living Monolith was created in 1969.
The population of Monolith Productions is 100.
Pokotia Monolith was created in 2001.