GNU Collaborative International Dictionary of English

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Found one definition

1.       
   Sinus (?), n.; pl. L. Sinus, E. Sinuses (#). [L., a bent surface, a curve, the folds or bosom of a garment, etc., a bay.  Cf. Sine, n.]
   1. An opening; a hollow; a bending.
   
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   2. A bay of the sea; a recess in the shore.
   
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   3. (Anat. & Zool.) A cavity; a depression. Specifically: (a) A cavity in a bone or other part, either closed or with a narrow opening. (b) A dilated vessel or canal.
   
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   4. (Med.) A narrow, elongated cavity, in which pus is collected; an elongated abscess with only a small orifice.
   
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   5. (Bot.) A depression between adjoining lobes.
   
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   ☞ A sinus may be rounded, as in the leaf of the white oak, or acute, as in that of the red maple.
   
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   Pallial sinus. (Zool.) See under Pallial. -- Sinus venosus (?). [L., venous dilatation.] (Anat.) (a) The main part of the cavity of the right auricle of the heart in the higher vertebrates. (b) In the lower vertebrates, a distinct chamber of the heart formed by the union of the large systematic veins and opening into the auricle.
   
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