Technically, ptyche (Greek) meaning fold, would or should apply to hinged
panels. Hinged meaning they fold.
I see the term quadriptych
used all the time for 4-panel works, but I believe like brynmr said, the term polyptych
is what should be used. The word quadriptych doesn't even come up on wikipedia or any other dictionary that I've tried. I think it's a "mixed-language" word for the sake of convenience. (Latin & Greek)
However the word tetraptych
is defined as: n. painting in four parts, especially hinged.
So from what I've seen, if you've got more than 3 panels you should use the word polyptych
, or say "multiple panels (x9)", "multi-panel works"... a nine-panel painting; a nine-panel work