We say 'szivárvány' in Hungarian. I've never thought it had an actual meaning other than rainbow, or what the root is, so I looked it up.
It comes from the verb szív 'to suck' because some people believed that rainbows suck up the rain and water from rivers.
It also meant sponge, pump well,suction-pump. All this was new information to me as well:D
(By the way, 'iris' is szivárványhártya, lit. 'rainbow membrane'.)