From HomoExcelsior

1. A depression or cavity formed by a bending or curving. 2. A dilated channel or receptacle containing chiefly venous blood. 3. Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils. 4. A fistula leading from a pus-filled cavity. 5. A recess or an indentation between lobes of a leaf or corolla.

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