plural sinuses
: any of several spaces in the skull that connect with the nostrils
—usually plural
My sinuses are blocked. [=they are filled with mucus that will not drain properly]
—often used before another nouna sinus infection/problem
Cite this Entry
“Sinus.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/sinus. Accessed 22 Jun. 2026.
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