noun

a feeling of guilt or moral scruple that prevents or follows the doing of something bad.

they used their tanks without compunction

scruples,misgivings,qualms,worries,unease,uneasiness,hesitation,hesitancy,doubts,reluctance,reservations,guilt,feelings of guilt,guilty conscience,pangs/twinges of conscience,remorse,regret,contrition,contriteness,self-reproach,repentance,penitence