1.hardened criminal/police officer etcEXPERIENCEDa criminal, police officer etc who has had a lot of experience of things that are shocking and is therefore less affected by them 慣犯/老練的警察等
2.become hardened (to something)USED TO/ACCUSTOMED TOto become used to something shocking because you have seen it many times(對某事)變得麻木[無動於衷]