'single-handedness' originates from English, formed by the adjective 'single-handed' plus the noun-forming suffix '-ness'. The element 'single' traces back to Proto-Germanic '*singlaz' (via Old English), where the root meant 'one' or 'not one of a pair'; 'hand' comes from Old English 'hand', meaning 'hand'; and the suffix '-ness' comes from Old English '-nysse' meaning 'state or quality'.

'single' developed from Proto-Germanic '*singlaz' into Old English forms and into Middle English 'single'; 'hand' remained from Old English 'hand'. The compound adjective 'single-handed' (meaning 'done by one person or with one hand') is attested in Early Modern English, and the abstract noun 'single-handedness' was later formed by adding '-ness' to name the quality or state.

Initially the compound could emphasize doing something with one hand (literal sense) or by a single person; over time the dominant sense broadened to denote acting alone or without assistance (figurative sense), which is the common modern usage.