noun
an ugly or unpromising child who grows into a beautiful or worthy person
• Hypernyms: ↑anomaly, ↑unusual person
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noun, pl ⋯ -lings [count]
: a person or thing that is not attractive or successful but that is likely to become attractive or successful in the future
The house is an ugly duckling, but it has a lot of potential.
an ugly duckling that has become a beautiful swan [=an ugly/unsuccessful person or thing that has become beautiful/successful]
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a person or thing that at first does not seem attractive or likely to succeed but that later becomes successful or much admired From the title of a story by Hans Christian Andersen, in which a young swan thinks it is an ugly young duck until it grows up into a beautiful adult swan.
Useful english dictionary. 2012.