'earthily' originates from English, specifically formed from the adjective 'earthy' plus the adverbial suffix '-ly'; the ultimate root is Old English 'eorþe' (eor- / eort-), where the root meant 'ground, soil'.

'earth' comes from Old English 'eorþe' (Middle English 'erthe'), which became modern English 'earth'; the adjective 'earthy' was formed in Middle English by adding the suffix '-y' to 'earth', and the adverb 'earthily' was later formed by adding '-ly' to 'earthy'.

Initially, the root referred specifically to the physical 'ground' or 'soil'; over time 'earthy' gained figurative senses of being 'coarse', 'worldly', or 'sensual', and 'earthily' came to mean 'in a coarse or unrefined manner' as well as the literal 'in an earth-related way'.