1650s, "of the nature of a disease, indicative of a disease," from Latin morbidus "diseased," from morbus "sickness, disease, ailment, illness," from root of mori "to die," which is possibly from PIE root *mer- "to rub, pound, wear away" (cognates: Sanskrit mrnati "crushes, bruises;" Greek marainein "to consume, exhaust, put out, quench," marasmus "consumption"). Transferred use, of mental states, is from 1777. Related: Morbidly; morbidness.