nether(beneath the earth's surface) adjective [UK: ˈne.ðə(r)] [US: ˈne.ðər]
underground(below the ground, see also: subterranean) adjective [UK: ˈʌn.də.ɡraʊnd] [US: ˈʌn.dər.ˌɡrɑːwnd]The plant has an underground stem. = La pianta ha un fusto sotterraneo.
sotterraneoadjective {m}
subterranean(below ground, under the earth, see also: underground) adjective [UK: ˌsʌb.tə.ˈreɪ.nɪən] [US: səb.tə.ˈreɪ.niən]