A young hawk, especially one that is still learning to fly and hunt.
From Old French 'niais' meaning 'nest-bound,' derived from Latin 'nidus' meaning 'nest.' The word entered English in the 14th century specifically for young hawks being trained for falconry.
Medieval falconers had a whole specialized vocabulary for different ages of birds—an eyass was the valuable trainee. Shakespeare used this word, showing how deeply falconry was woven into educated culture.
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