ivory nut

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The seed of any of various tropical American palms of the genus Phytelephas, having a hard white endosperm that is the source of vegetable ivory, used for carving and manufacturing buttons.

from The Century Dictionary.

• noun The seed of Phytelephas macrocarpa, a low-growing palm, native of South America.

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

• noun nutlike seed of a South American palm; the hard white shell takes a high polish and is used for e.g. buttons