The English word torpor is a 13th-century borrowing from Latin: torpōr-, torpor mean "numbness, paralysis, absence of energy, lethargy," and correspond to the Latin verb torpēre, meaning "to be numb, lack sensation; to be struck motionless; to be sluggish or lethargic." Early use of the English word is found in a 13th-century guide for religious recluses, where it refers to a spiritual or intellectual lethargy, but scant evidence of the word appears between that point and the 1600s, when the word began to be used in reference to both mental and physical sluggishness. The related adjective torpid (from the Latin adjective torpidus, meaning "numbed" or "paralyzed") has since the 15th century been used to mean "numb," but today it more often means "lacking in energy or vigor."