尖儿 is the erhua-suffixed (
儿化) Beijing-flavored form of
尖 — colloquial, spoken, northern. Three live senses: (1) physical tip (
笔尖儿 pen-tip,
鼻尖儿 nose-tip), (2) the outstanding one ('cream of the crop' —
班里的尖儿,
顶尖儿), (3) Beijing/Peking opera term for a soaring high note. The non-erhua
尖 covers the same meanings but in formal / standard register.