It's not an acronym, or an abbreviation, but just one of a whole host of three-letter codes in the Q-Code system. I think Aussie's answer is simply the result of somebody finding some words that fit - almost. After all, QNH has nothing to do with height.
The system originated in the days of morse code, where a simple three-letter code could replace perhaps a lengthy sentence, and save a lot of time. It also meant the message could be understood instantly, in any language, and without any ambiguity.
I'm guessing it's a Q code because there are no three-letter English words that begin with Q, so as soon as one is received it is obvious that it has a special meaning.