肢 means 'limb'

Characters for body parts often feature 月 radicals. That's true here, but these four kanji have much more in common. First, limbs and joints are prone to soreness, injury, and disability, requiring various healing modalities. Second, the shoulders, elbows, and knees can show how we're relating to other people; the Japanese associate these body parts with lending support, sitting close for an intimate talk, and reining in someone's behavior. Those body parts also play roles in martial arts and sumo. Finally, one's stance can express seriousness, tension, pride, shame, discouragement, respect, remorse, or a lack of reservedness.