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si·nus

(sīnəs)

1. A depression or cavity formed by a bending or curving.

2. Anatomy

a. A dilated channel or receptacle containing chiefly venous blood.

b. Any of various air-filled cavities in the bones of the skull, especially one communicating with the nostrils.

3. Medicine A fistula leading from a pus-filled cavity.

4. Botany A recess or indentation between two lobes or segments, as of a leaf.

[Middle English, hollow in the body, from Medieval Latin, from Latin, curve, hollow.]

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sinus

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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