from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A small gas bubble in igneous, especially volcanic, rock filled with secondary minerals such as zeolite, calcite, or quartz.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A rounded mass of secondary mineral found in volcanic rock
from The Century Dictionary and Cyclopedia
- n. One of the crystalline nodules found in amygdaloid (which see).
Latin amygdala, almond (from its shape); see amygdala + (nod)ule.(American Heritage® Dictionary of the English Language, Fourth Edition)