The term 'duckling' specifically refers to ducks that are very young, typically still with their fluffy down. The duckling's down was so soft, unlike the feathers of adult ducks.
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Animal Offspring
'Duckling' highlights the relationship between young animals and their parents, often seen together. I saw a line of ducklings following their mother at the park.
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Metaphorical Use
Metaphorically, 'duckling' can describe something small or immature, sometimes even affectionately. He's the duckling of the team, always eager to learn from the others.