Which Greek philosopher first used a word meaning uncuttable to describe matter?

The Greek philosopher who first used a word meaning "uncuttable" to describe matter was Democritus.

He called these uncuttable particles "atomos", which is the Greek word for "uncuttable" or "indivisible". Democritus believed that all matter was made up of these tiny, indestructible particles.

While Democritus' theory was not widely accepted in his lifetime, it laid the groundwork for the modern understanding of atoms.