n. pl. tes·ser·ae (tĕsə-rē′)
One of the small squares of stone or glass used in making mosaic patterns.
[Latin, from Greek, neuter of tesseres, variant of tessares, four; see kwetwer- in the Appendix of Indo-European roots.]
(click for a larger image)tessera
c. 450 bc mosaic mask made with turquoise, coral, and stone tesserae
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Indo-European & Semitic Roots Appendices
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