YEARS  AGO
  Neolithic (new stone) is a word that describes a time known as the New Stone Age.  It comes before the Bronze Age when metal became more widely used.

Megalith literally means GREAT STONE.  It comes from ancient Greek words. 

Megalithic is a term used to describe buildings or constructions that are made of large stones, and is usually reserved for buildings that are very old.  Stonehenge, Newgrange in Ireland and the temples on Malta are all megalithic.   There are also megalithic tombs in other parts of Europe.

What makes a stone large enough to be a megalith? Generally it is something that would take a team of people to move.  The largest stone in Malta's temples is estimated to weigh about nineteen tons -- about the same weight as an 18-wheeler truck.

A monolith is a stone that stands alone, such as an obelisk.

Wayland's Smithy, megalithic tomb, UK
 

   
Mnajdra Temple, Malta