A cavity or chamber in the body, especially one found in bone; most commonly refers to the maxillary sinus in the cheekbone.
From Latin 'antrum' (cave, cavity). Borrowed directly from Latin into medical English in the 16th century, it retained its literal meaning of a hollow space or cave.
Your skull isn't solid—it's full of air-filled caves called antra that make your head lighter and help your voice resonate, and they're named after actual caves because they literally are hollow spaces in bone!
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