A small piece of wood

One word substitute is Chip.

Splinter: a small, thin, sharp piece of wood, glass, or similar material broken off from a larger piece.
Crumb: a small fragment of bread, cake, or biscuit.
Scrap: a small piece or amount of something, especially one that is left over after the greater part has been used.
Chip: a small piece of something removed in the course of chopping, cutting, or breaking a hard material such as wood or stone.