'torpedo-defense' originates from English, specifically the compound of 'torpedo' and 'defense'. 'torpedo' in English comes ultimately from Modern Latin 'torpedō' (from Latin 'torpēre' meaning 'to be numb'), originally the name for the electric ray (a fish); 'defense' comes from Old French 'defense', from Latin 'defendere' meaning 'to ward off'.

'torpedo' changed from the Latin root 'torpēre' (concept of numbness) into Latin/Modern Latin forms such as 'torpedō', was used for the electric ray and later (19th century) for the naval explosive device 'torpedo'. 'defense' passed from Latin 'defendere' into Old French 'defense' and Middle English 'defence', evolving into modern English 'defense/defence'.

Initially, 'torpedo' referred to numbness/the electric ray and later came to denote the explosive naval weapon; 'defense' originally meant the act of warding off and has retained that core sense. The compound now means systems or measures to protect against torpedoes.