sinus

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. A bend or fold; a curving part of anything; a sinuosity; specifically, a bay of the sea; a gulf.
2. n. In anatomy and zoology, a cavity or hollow of bone or other tissue, in the widest sense; a bay, recess, pocket, dilatation, or excavation, generally deeper and less open than a fossa: used with either English or Latin context. Specifically— A hollow or excavation in a bone of the skull; an air-sinus. Such sinuses are larger than the spaces which constitute cancellation, or the spongy tissue of bones (see cancellate ), and most of them are specified by qualifying terms. See phrases below, and cuts under eyeball, craniofacial, and diploë.
3. n. In pathology, a narrow passage leading to an abscess or other diseased locality; a fistula.
4. n. In botany, the recess or rounded curve between two projecting lobes: as, the sinuses of a repand or sinuate leaf. See cuts under kidney-shaped, pinnatifid, repand, and sinuate.
5. n. The bony air-sinuses of the head. See def. 2 .
6. n. The rhombocœlia. Also called sinus rhomboidalis.
7. n. one of the sinuses of the dura mater (see above), or
8. n. a sinus venosus (see above).

Wiktionary

1. n. anatomy A pouch or cavity in any organ or tissue, especially the paranasal sinus.
2. n. pathology An abnormal cavity or passage such as a fistula, caused by the destruction of tissue.

GNU Webster's 1913

1. n. An opening; a hollow; a bending.
2. n. A bay of the sea; a recess in the shore.
3. n. (Anat. & Zoöl.) A cavity; a depression.
4. n. A cavity in a bone or other part, either closed or with a narrow opening.
5. n. A dilated vessel or canal.
6. n. (Med.) A narrow, elongated cavity, in which pus is collected; an elongated abscess with only a small orifice.
7. n. (Bot.) A depression between adjoining lobes.

WordNet 3.0

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