Underground (adjective / adverb / noun) — تحت الأرض: Beneath the ground; also secret; in Britain, an underground railway. Below are 7 words with a similar meaning; the linked ones have full GL Dictionary entries with their meaning in Arabic.
subterraneanburiedcoverttubemetro
The lowest floor of a building; an underground room; a cellar; a foundation level; below-ground space
Situated directly below; also beneath the surface.