Nuts and Bolts: metro.

What does metro mean?

All sorts of things.

Metro itself, the small urban railway that sometimes runs underground, is short for the French chemin de fer métropolitain.

So how about metropolitan, then? That's from the Greek mētēr, mother, and means, literally, mother city.

In metrorrhagia, though, metro is from a different Greek word, mētra, which means womb. 

Metronome? From the Greek metron, which means measure.

Metronidazole? (It's a medicine.) Cobbled together from me(thyl ni)tro n (im) id (e) azole.

Metrongagen? (The phenomenon that the weather forecast is not necessarily to be relied upon.) From Met (Office is w)rong ag(ain) en.

Okay, I made that last one up. But why not? Everyone else seem to be doing it.