1. adjective Resilient or impervious to bullets, as of fabric or other material. That bulletproof vest saved my life!

2. adjective Resistant to mishandling, abuse, damage, error, or malfunction. Don't worry about breaking the phone, these new models are bulletproof! We've developed a bulletproof computer program that even the most non-computer-savvy person will be able to use!

3. adjective Extremely well planned or thought out, such as to be impervious to criticism or failure. We have a bulletproof plan for tackling poverty in the neighborhood. My thesis proposal is absolutely bulletproof.

4. verb To make resilient or impervious to bullets, as of fabric or other material. After crime rates rose in the city, many stores began bulletproofing their windows and doors.

5. verb To make resistant to mishandling, abuse, damage, error, or malfunction. Don't worry about breaking the phone, these new models have been totally bulletproofed! We've bulletproofed our latest computer program so that even the most non-computer-savvy person will be able to use it!

6. verb To plan or think something out so well as to be impervious to criticism or failure. Make sure you bulletproof your plan before you submit it to the developers. I spent an extra two weeks totally bulletproofing my doctoral thesis.