'undestroyable' originates from English, formed by the negative prefix 'un-' (Old English 'un-') meaning 'not' combined with the adjective-forming suffix '-able' attached to the verb 'destroy', which ultimately comes from Latin 'destruere' where 'de-' meant 'down/away' and 'struere' meant 'to build or pile'.

'destroy' entered English via Old French (e.g. 'destruire') from Latin 'destruere'; Middle English had forms like 'destroyen' and 'destroy', and Modern English formed 'destroyable' (destroy + -able), to which 'un-' was added to create 'undestroyable'.

Initially the Latin root conveyed the sense 'to overturn/tear down' (from 'destruere'), and over time the compound 'undestroyable' has carried the straightforward modern meaning 'not able to be destroyed' (similar in sense to 'indestructible').