Jarl : O.N. ~ originally meant a warrior, but came to mean a war-leader, and finally became a title of rank equal to that of an Earl.
Jörmun : O.N. ~ usually to mean something super-natural of great size and/or power. Jormungand is the World-Serpent who resides in the Great Ocean which encompasses MidgardR, all the while biting its own tail. Jormunsol, (Irminsul), is the symbol of Yggradsil and Tyr which represents cosmic order, and is the column which symbolically holds up the World and/or the Universe.
Jötunn : O.N. ~ a being of great strength & longevity, taking shape in all sizes and forms. Suggestions indicate they have the ability to shape-change at will.