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Jyutping mang4 mang4 daat6
Pinyin méng méng da

Definitions (Wiktionary)
  1. adj, neologism, slang
    very cute; adorable; adorkable

萌萌噠 [--哒]

Jyutping
Pinyin méng méng dā

Definitions (CC-CEDICT)
  1. (Internet slang) adorable
  2. cute