Definition of "sinus" [si•nus]

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

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "WATERS: The first question I had, and I am sure the Fords are asking the same question too, the president was at Hahnemann Hospital last night complaining of what he described as a sinus infection and wax buildup in the ear."
• "The coalescence of the neural folds occurs first in the region of the hind-brain, and from there extends forward and backward; toward the end of the third week the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess which is in contact, for a time, with the overlying ectoderm; the hinder part of the neural groove presents for a time a rhomboidal shape, and to this expanded portion the term sinus rhomboidalis has been applied (Fig. 18)."
• "KNOX: That, he says, will be the next big advance in sinus treatment."