'bacterioscopically' originates from modern English, formed from the adjective 'bacterioscopic' plus the adverbial suffix '-ally'. 'bacterioscopic' itself combines the prefix 'bacterio-' (from Neo-Latin 'bacterium', from Greek 'bakterion') meaning 'rod (small staff)' and the suffix '-scopic' (from Greek 'skopein') meaning 'to look'.

'bacterioscopically' developed from the adjective 'bacterioscopic' coined in the 19th century within scientific/medical English; 'bacterium' came into Neo-Latin from Greek 'bakterion', and the combining form '-scopic' derives from Greek 'skopein' via New Latin and modern scientific formation.

Initially, it meant 'pertaining to the observation of bacteria', and over time it has retained that specific sense as 'in a manner of observing bacteria (by bacterioscopy)'.