expression, noun
ugly duckling
Idiomatic expression referring to a person or thing that initially seems unattractive or unpromising but later develops into something beautiful or successful. Originates from the Hans Christian Andersen fairy tale.
彼女は子供の頃はみにくいアヒルの子だったが、今では有名なモデルだ。
She was an ugly duckling as a child, but now she's a famous model.
この会社はみにくいアヒルの子から業界のリーダーに成長した。
This company grew from an ugly duckling into an industry leader.
Means 'ugly' or 'unsightly' as an adjective; the phrase みにくいアヒルの子 is a fixed expression, not a literal description.
From the title of Hans Christian Andersen's fairy tale 'The Ugly Duckling' (Den grimme ælling), translated into Japanese as みにくいアヒルの子.