'subterraneously' originates from Latin, specifically the word 'subterraneus,' where 'sub-' meant 'under' and 'terra' meant 'earth.'

'subterraneus' transformed into the Medieval Latin word 'subterraneus,' and eventually became the modern English word 'subterraneous' with the adverbial form 'subterraneously.'

Initially, it meant 'under the earth,' and this meaning has largely remained the same in modern usage.