'applicability' originates from Latin, specifically the verb 'applicare', where the prefix 'ad-' (assimilated to 'ap-') meant 'to/toward' and the root 'plicare' meant 'to fold or to attach'.

'applicare' passed into Late Latin as 'applicabilis' (able to be applied) and through Old French and Medieval Latin forms influenced English, later becoming the English adjective 'applicable' and the noun 'applicability'.

Initially it referred to 'the action of applying or attaching'; over time it shifted to denote the quality or degree to which something can be applied — its current meaning of 'suitability or relevance'.