Ma'anar ƙamus na kalmar "laifi na babban laifi" yana nufin wani laifi da ke da hukuncin kisa. Laifi ne mai tsanani wanda ake ganin shi ne mafi girman nau'in laifi kuma yana da hukunci mafi tsanani da doka ta tanada. Laifukan manyan laifuka na iya haɗawa da laifuffuka kamar kisan kai, cin amanar ƙasa, leƙen asiri, ko wasu nau'ikan ta'addanci, dangane da hukumci da tsarin shari'a da ake magana akai. Kalmar “babban birni” a wannan mahallin ta samo asali ne daga kalmar Latin “capitalis,” wanda ke nufin “kai,” kuma yana nufin cewa hukuncin irin waɗannan laifuka a tarihi ya ƙunshi fille kai.