A young bird that has just grown feathers and is learning to fly, or a young, inexperienced person.
From 'fledge' plus the diminutive suffix '-ling' (little one). Originally meant only young birds, but became a metaphor for any inexperienced youth.
The suffix '-ling' is delightful—'fledgeling' is literally 'little-fledged-thing,' which perfectly captures that in-between stage where you're almost ready but still learning!
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