tessera

noun, plural tes·ser·ae [tes–uh-ree] /ˈtɛs əˌri/.

1. one of the small pieces used in mosaic work.
2. a small square of bone, wood, or the like, used in ancient times as a token, tally, ticket, etc.

noun plural -serae (-səˌriː)

1. a small square tile of stone, glass, etc, used in mosaics
2. a die, tally, etc, used in classical times, made of bone or wood

n.plural tesserae, 1650s, from Latin tessera, from Ionic Greek tesseres (Attic tessares) “four” (see four).