from
The Collaborative International Dictionary of English v.0.48
bullet-proof \bul"let-proof`\, bulletproof \bul"let*proof`\, a.
1. Capable of resisting the force of a bullet; resistant to
penetration by a bullet; armored; as, a bulletproof vest;
a bulletproof window.
[1913 Webster +PJC]
2. designed so as to be resistant to abuse or misuse and
incapable of malfunction under normal use; as, a
bulletproof computer program.
[PJC]
3. so well thought out as to be resistant to criticism or
certain to succeed; as, a bulletproof plan.
[PJC]