They are really not all that different. "Iffy" creates the notion that something is in the gray area, that it could go either way.Originally Posted by Francois
Simon hasn't made up his mind. He might go to Columbia; he might not.
The milk might be spoiled but it might be OK. The sniffere can;t really tell.
The weather might be OK, but it might get bad. The speaker doesn't really know.
Both meanings are used, but the word itself is not all that common. It is very informal, IMO.