Torpid comes from Latin torpidus ('numb, sluggish'), from torpēre ('to be stiff or numb'). The form is best read as a historical transfer or inheritance, with its older language material carrying the main semantic load. As an adjective, it carries the sense "sluggish, inactive, or mentally dull; lacking energy", with the older formation still helping explain the modern use. Relevant historical forms include Latin torpidus, Latin torpēre, and Proto-Indo-European *sterp-. Derivative forms include torpidly, torpidity, torpidness; related words include torpor, torpedo.