Jonah (4)
I believe the answer is:
jinx
'jonah' is the definition.
(I know that jonah can be written as jinx)
This is all the clue.
(Other definitions for jinx that I've seen before include "Evil spell" , "Bringer of bad luck" , "Hex or voodoo" , "Curse" , "Thing or person that brings bad luck" .)