ク, くる.しい, ぐる.しい, くる.しむ, くる.しめる, にが.い, にが.る
suffering, trial, worry, hardship, feel bitter, scowl
JLPT3 G3 S8 F623
古# hard; dried out + 艸 grass/plant → *bitter* plant that makes the mouth go dry → *stubborn*; *pain*; *agony*; *suffering*; *hardship*; *trying* (experience); *exert oneself*; *worry*; *distress*; *pressure*; *torment*; *torture*; *be at a loss*; *embarrassment*.
[Full Kanji Etymology List]