nicker nut

Wiktionary

1. n. The rounded seed of the nicker tree.

GNU Webster's 1913

1. 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 Cæsalpinia. Cæsalpinia Bonduc has yellowish seeds; Cæsalpinia Bonducella, bluish gray.

WordNet 3.0

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