If someone is dressed to be kill, he or she is dressed in a very glamorous and impressive manner. (to be) dressed to kill 不是穿着衣服去作杀手，而是说一个人穿着出众，打扮时尚。这个俚语的来源是当人们的打扮很出众时，会说她kill (dominate, knock over) someone, 就如同中文中所说“迷死众生”。

Examples:

Tina was dressed to kill for her date on Saturday night. 周六的晚上，蒂娜打扮得漂漂亮亮地去赴约。

The sales manager spent a bundle of money on fashionable new clothes and always wanted to be dressed to kill when she made a sales presentation to clients. 销售经理每月都要花大笔钱购买新时装，总想在向客户做销售演示时衣着光鲜。