warrior, arms, savage, Ainu
戉 centers on a large bladed weapon and the warrior who wields it. The meanings 'arms' and 'warrior' follow directly from this weapon, while 'savage' and 'Ainu' are historical applications of the same idea to describe a people seen as fierce outsiders.
戉 is a pictograph of a large battle-axe or halberd. The modern form preserves the blade and handle shape, with the diagonal stroke representing the weapon's head.
The shape resembles a heavy axe with a long handle and a curved blade. Picture a warrior holding this weapon, ready for battle.
For ジュウ, imagine a warrior named Jew wielding the axe: Jew -> ジュウ, and his weapon is the 戉.