gravamen (n.)

1640s, "grievance," from Late Latin gravamen "trouble, physical inconvenience" (in Medieval Latin, "a grievance"), literally "a burden," from Latin gravare "to burden, make heavy, weigh down; oppress," from gravis "heavy" (from PIE root *gwere-(1) "heavy"). Specifically, in law, "part of the accusation which weighs most heavily against the accused." Related: Gravaminous.