A word that has no ture definiton because of the fact that it means so many different things. When you use this word in a conversation the only way for it to make sense is for the other person to at least be somewhat knowlegeable in the topic you are talking about. It usually is something that you will find in a video game. In one case Sentinel is actually the name of a video game for ps1. If you use this word when talking to someone about video games that isn't very knowlegeable but pretends they know what they are talking about, they will not even think for a split-second that what your are saying isn't true. Even people who know video games might get fooled if you just slip this wor din to your conversation because of normal it will sound. Typing this word in on google will bring up 7,500,000 links. This pretty much speaks for itself.
In 007 the sentinel is a missle launcher, In GTA the sentinel is a car,
In Halo the sentinels are flying machines that attack with laser-like weapons,
In Half-life the sentile is a machine gun,
Im sure in at least a few games out there besides Halo where there is an enemy(s) known as the Sentinel. If I wasn't so lazy I could probably find more examples via google (holy shit 7,500,000 links!) As you can see there is no true definiton for sentinel.