'deflectibility' originates from Latin, specifically the verb 'deflectere', where 'de-' meant 'away' and 'flectere' meant 'to bend'. The English noun is formed by the root 'deflect-' plus the nominalizing suffix '-ibility' (via Latin '-ibilis' and Old French '-ibilité').

'deflectibility' evolved from the adjective 'deflectible' (formed in English from 'deflect' + '-ible'), where 'deflect' was borrowed into English from Late Latin 'deflectere' (and related Old French forms). The suffix '-ibility' came into English through Latin and Old French nominal formations, producing 'deflectibility' to denote the quality or state.

Initially the Latin root referred to the physical action 'to bend away'; over time English formed abstract nouns like 'deflectibility' to mean the property or capability of being bent, turned aside, or deviated from an intended course.