c.1520, "electric ray," from L. torpedo,
originally "numbness" (from the effect of being jolted by the ray's electric discharges), from torpere
"be numb" (see torpor
). The sense of "explosive device used to blow up enemy ships" is first recorded 1776, as a floating mine; the self-propelled version is from 1860s. The verb is first recorded 1873; the fig. sense is attested from 1895.