underlying \| ̷ ̷ ̷ ̷| ̷ ̷ ̷ ̷\adjective Etymology: from present participle of underlie 1. a.: lying under or beneath < the underlying strata > b.: implicit, fundamental < underlying principles > 2.: innate or organic but evident only on close inspection < underlying identity about the motley immigrants > 3.: anterior and prior in claim < underlying mortgage >