'fissionability' originates from Modern English, specifically the word 'fission' + the suffix '-ability', where 'fission' meant 'a splitting' and '-ability' meant 'capacity' or 'state of being able'.

'fission' changed from Latin/Medieval Latin 'fissio' (from Latin 'findere'/'fissus', meaning 'to split' or 'split') and entered scientific English in the 19th century; 'fissionability' was formed later in English by combining 'fission' with the productive suffix '-ability' to denote the property or capacity.

Initially it referred generally to 'the act or process of splitting', but over time in scientific contexts it evolved into the specialized sense 'the capacity to undergo nuclear fission', which is the current primary usage.