Why are the chess pieces called what they are?

An army from India

In the Persian form of the game, the pieces had these names, according to the chess historian H. J. R. Murray.

The game's oldest name, chaturanga, means roughly "four parts": the elephants, chariots, horsemen, and infantry of an Indian army.

The queen

The counselor became a queen in Europe, probably because the piece stood beside the king, Murray wrote. The oldest record of the piece as a queen is a Latin poem from around 997. At the time it was still weak and moved only one square diagonally. How she became the strongest piece is under How old is chess?

In English, the chess queen has had that name since around 1400.

The rook

The Persian rukh meant chariot, according to Murray. Others have suggested other meanings, so not everyone agrees. English has said rook since around 1300, from the Old French roc.

The old French name lives on in another language's word for castling: the French roquer comes from roc, and Swedish borrowed it as rockera.

The bishop, the knight, and the pawn

The elephant was al-fīl in Arabic, and in medieval English the piece was the alfin. It has been the bishop in English since the 16th century. Other languages went other ways: in German and Swedish it's a runner, Läufer and löpare.

The horse became a horseman, and the horseman was soon taken for a feudal knight, Murray wrote. In English, the chess knight has been so called at least since the 15th century. In German and Swedish it's a jumper, Springer and springare.

Pawn goes back through Anglo-French poun to the Medieval Latin pedonem, a foot soldier, just like the Persian name. How the pieces move is in the chess rules.