WordNet sense 1 (situated at the bottom or lowest position):

bottom

WordNet sense 2 (dwelling beneath the surface of the earth):

chthonian, chthonic

WordNet sense 3 (being of a lower world of the dead):

infernal

WordNet sense 4 (located below or beneath something else):

under

WordNet sense 5 (literal meanings; being at or having a relatively small elevation or upward extension):

low