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Sioux
Sioux City
Sioux Falls
sip
SIPC
siphon
siphon bottle
siphonophore
siphonostele
siphuncle
SIPP
sippet
sipunculid
SIR
Sir
sir
sirdar
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sinus

si·nus [ snəss ] (plural si·nus·es)


noun 
Definition:
 
1. cavity in bone of skull: a cavity filled with air in the bones of the face and skull, especially one opening into the nasal passages

2. channel for blood: a widened channel containing blood, especially venous blood

3. channel leading from body cavity: an elongated tract leading from a pus-filled region of the body to the exterior or to the cavity of a hollow organ

4. notch between leaves: a cleft or indentation between the lobes of a leaf or the fused petals of a corolla

[15th century < Latin, "curve, fold, hollow"]
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