late 15c., "austerity or strictness of life," from Middle French severite, from Latin severitas "seriousness, strictness, sternness," from severus "stern, strict, serious," of uncertain origin, probably from PIE root *segh- "to have, hold," on the notion of "steadfastness, toughness." Meaning "strictness in dealing with others" is recorded from 1520s.
