In a state of brooding; sitting on eggs to hatch them, or contemplating something deeply.
From 'a-' (in a state of) + 'brood' (to sit on eggs, or to think deeply). The 'a-' prefix creates an adjective from the verb 'brood.'
The double meaning of 'abrood'—simultaneously sitting on eggs and lost in thought—shows how humans project their inner contemplation onto birds' physical actions.
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