nicker nut

from the GNU version of the Collaborative International Dictionary of English.

• 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The rounded seed of the nicker tree.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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