Lifesaver
Part of speech: noun
Definition: Someone or something that saves lives. Someone or something that is very useful or helpful.
Lifeguard
Part of speech: noun
Definition: an attendant, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of watera lifesavera sturdy metal bracket affixed in front of each of the leading wheels of a train to deflect small objects away from the wheels to prevent derailment.
Example sentence: Let me put it this way, if you were drowning, you wouldn't really be in a place to lend a hand as far as being rescued. You'd be at the mercy of the lifeguard. Once pulled out, you may be a little out of it, not sure where you are, but safe nonetheless.