It's funny to consider that one of the canonically great philosophers in history is known essentially by the equivalent of his WWE wrestling name. It's like if in the future there were classes taught on the philosophical ideas of "The Rock".
Modern english words that stem from the same root: plateau, platitude, plat, plate -- via French and Latin (plattus) from Greek (platis "flat, wide, broad").
Exactly what he meant has led to centuries of debate between protestants and catholics.