'detachableness' originates from English built on the adjective 'detachable', which in turn derives from the verb 'detach'. 'Detach' comes via French 'détacher' (from Old French) and ultimately from Latin elements (de- meaning 'off, away' + a form meaning 'to fasten/attach').

'detach' entered English from French 'détacher'; English formed 'detachable' by adding the suffix '-able' and then the noun-forming suffix '-ness' produced 'detachableness' to denote the state or quality.

Initially, the verb 'detach' meant 'to unfasten, separate, or remove'; over time the derived adjective and noun forms came to denote the capability or quality of being separated — now expressed by 'detachableness' as 'the quality of being detachable'.