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Jyutping sing2 muk6 zai2
Pinyin xǐng mù zǎi

Definitions (粵典–words.hk)
  1. 名詞
    對​一​啲​連好​基本​嘅​嘢​都​做​唔​到​、​蠢蠢​鈍​鈍​咁​,​但​又​唔​係​真​係​有​智力​障​礙​嘅​人​嘅​稱​呼
    a dim-witted person, literally "clever boy"
Definitions (Wiktionary)
  1. noun, Cantonese
    clever boy; smart boy
Definitions (Kaifangcidian)
  1. 聰明人 – 聪明人
  2. 小機靈 – 小机灵
  3. 機靈鬼 – 机灵鬼

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Jyutping sing2 muk6 zai2
Pinyin xǐng mù zǐ

Definitions (CC-CANTO)
  1. (noun) a clever boy or kid; smart boy