'anaerobically' originates from 'anaerobic', which comes from the Greek prefix 'an-' meaning 'without' and 'aer' meaning 'air', combined with '-ic' and '-ally' to form the adverb.

'anaerobic' was formed in the 19th century from Greek roots, and 'anaerobically' was later derived as the adverbial form in modern English.

Initially, it meant 'without air (oxygen)', and over time it evolved into its current scientific meaning of 'in the absence of oxygen'.