'antarctic' originates from Greek, specifically the word 'antarktikos', where the prefix 'anti-' meant 'opposite' and 'arktos' meant 'bear'.

'antarctic' passed into Latin as 'antarcticus' and then into English (via Medieval/Modern Latin and French influence) to become the modern English word 'antarctic', with the adverb formed by adding '-ally'/'-ally' -> 'antarctically'.

Initially it meant 'opposite of the Arctic' (i.e., opposite the region of the bear/Arctic), but over time it evolved into its current geographic meaning of 'relating to the region around the South Pole' and, by extension, 'in the manner of that region'.