Princeton's WordNet

1. truffle, earthnut, earth-ball(noun)

   any of various highly prized edible subterranean fungi of the genus Tuber; grow naturally in southwestern Europe

2. earthball, false truffle, puffball, hard-skinned puffball(noun)

   any of various fungi of the genus Scleroderma having hard-skinned subterranean fruiting bodies resembling truffles