Definition of "Earthnut" :

noun: edible subterranean fungus of the genus Tuber

noun: pod of the peanut vine containing usually 2 nuts or seeds; groundnut' and monkey nut' are British terms

noun: a common European plant having edible tubers with the flavor of roasted chestnuts

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