adit (n.) Look up adit at Dictionary.com
"entrance," especially "horizontal mine excavation," c. 1600, from Latin aditus "an approach, an entrance; a going to or drawing near," from past participle stem of adire "to approach," from ad "to" (see ad-) + ire (past participle itus) "to go," from PIE root *ei- (1) "to go" (see ion).