tough, blunt

艮 depicts a man twisting his head and opening his eyes. When someone twists his head, his neck reaches its limit and hardly move, so艮 is used to describe something tough and still. On the other hand, 艮 has several meanings, it also means limit, boundary and difficulty, but those meanings have been replaced by限, 垠 and艱 respectively. Now艮 is seldom used independently, it exists as component of the others words.