If someone, especially a woman, is dressed to kill, they are wearing very smart or attractive clothes which are intended to attract attention and impress people.
To dress in extravagantly fancy or stylish clothes so as to thoroughly impress others.
#1 – Dressed Up for a Date
Jasmin: It must be a very special event that Stephen is taking you tonight. You’re dressed to kill!
Therese: Yes, he’s taking me to a fine dining on a cruise ship. It’s an elegant place so I did my best to put on something nice.
Jasmin: You look gorgeous. I hope you have a great time!
Therese: Thank you. I’m sure I will.
#2 – Going to Attend a Celebrity Party
Abby: Hey Cate, are you going to that fancy party next Saturday night?
Cate: The one in Beverly Hills for the movie producers? I wouldn’t miss it.
Abby: Yes, that’s the one. I’m wondering about what to wear.
Cate: Well, you better dress to kill cuz’ it’s going to be one extravagant party!