Lacking a nucleus, or describing a cell that has no nucleus (most famously, mature red blood cells).
From prefix 'a-' (meaning 'without') plus Latin 'nucleus' (meaning 'kernel' or 'nucleus'); literally 'without a nucleus'.
Red blood cells are the weirdest cells in your body—they dump their nucleus to fit more hemoglobin and carry more oxygen, making them anucleate superheroes of oxygen delivery.
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