'antitorpedo' originates from the Greek prefix 'anti-' meaning 'against' combined with the English word 'torpedo', which ultimately derives from Latin 'torpere' (via Italian 'torpedine'); 'torpere' meant 'to be numb or stiff'.

'torpedo' originally referred to the electric ray in Latin, later via Italian 'torpedine' it came to denote the naval weapon; English formed the compound 'antitorpedo' by adding the prefix 'anti-' to indicate opposition or protection against torpedoes.

Initially the parts meant 'against' + 'torpedo (originally the electric ray, later the weapon)'; over time the compound came to mean specifically 'designed to defend against torpedoes' in a naval/technical context.