'single-flagellated' originates from Modern English as a compound of 'single' (from Old English roots meaning 'one, alone') and 'flagellated', which in turn comes from Latin 'flagellum', where 'flagellum' meant 'whip'.

'flagellated' developed from Latin 'flagellum' into Late/Neo-Latin and Medieval Latin forms (e.g. 'flagellatus' meaning 'whipped' or 'having a whip-like organ'), then entered scientific English as 'flagellate' and its adjective form 'flagellated'; 'single' has Germanic/Old English origins and has long been used in English as 'one' or 'alone', producing the compound 'single-flagellated' in modern biological usage.

Initially, the root 'flagellum' referred to a 'whip'; over time, in biological terminology it came to mean a 'whip-like appendage' of cells, and 'single-flagellated' came to mean specifically 'having one such appendage'.