• 器用きよう — skillful / dexterous
• 器具きぐ — equipment / utensil
• 食器しょっき — tableware
• 楽器がっき — musical instrument
• 武器ぶき — weapon
• 容器ようき — container / receptacle
• 器量きりょう — capacity / caliber

器 shows multiple 口くち (openings), suggesting a vessel. From literal containers it extended to figurative “capacity” or “aptitude.”