bonduc nut, nicker nut, nicker seed(noun)

hard shiny grey seed of a bonduc tree; used for making e.g. jewelry

Nicker nut(u)

a rounded seed, rather smaller than a nutmeg, having a hard smooth shell, and a yellowish or bluish color. The seeds grow in the prickly pods of tropical, woody climbers of the genus Caesalpinia. C. Bonduc has yellowish seeds; C. Bonducella, bluish gray