Sinus word meaning and definition

[noun] a wide channel containing blood; does not have the coating of an ordinary blood vessel
[noun] any of various air-filled cavities especially in the bones of the skull
[noun] an abnormal passage leading from a suppurating cavity to the body surface

\Si"nus\, 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. 2. A bay of the sea; a recess in the shore. 3. (Anat. & Zo["o]l.) 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. 4. (Med.) A narrow, elongated cavity, in which pus is collected; an elongated abscess with only a small orifice. 5. (Bot.) A depression between adjoining lobes. Note: A sinus may be rounded, as in the leaf of the white oak, or acute, as in that of the red maple. {Pallial sinus}. (Zo["o]l.) 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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