the word 'underworld' is a transparent compound formed from two native old english elements: 'under' and 'world'. its literal meaning, 'the world beneath', was first applied in mythology to describe the subterranean abode of the dead, such as hades in greek mythology or hel in norse belief. this concrete, spatial concept was later extended metaphorically in the late 19th century to refer to the hidden, subterranean-like realm of criminal society, which operates beneath the surface of respectable, lawful society. the semantic logic thus evolved from a physical 'world below' to a figurative one, both sharing connotations of being concealed, separate, and often sinister.

Structure: under + world under (old english, meaning 'beneath, below'); world (old english, meaning 'human existence, the earth, age')