What does sinus mean?
A sinus is a cavity, hollow, or passage within a larger structure. Its best-known use is anatomical: the paranasal sinuses are air-filled spaces in and around the nose that may become inflamed or infected, producing sinus pain and congestion. The word can also describe a hollow within a bone or another organ. In botany, a sinus is an indentation or space between the lobes of a leaf, such as those that make an oak leaf deeply divided. Although the word may sound unusual to some speakers, it is firmly established in medical and scientific English. The broader idea is of a curved, recessed space: the Latin root meant a bend, fold, curve, or hollow. Today, "sinus" is most useful when describing the body’s connected cavities and related medical conditions, while its botanical sense remains more specialized.
nounIn anatomy, a sinus is a cavity or hollow passage in an organ or tissue, especially one of the air-filled spaces connected to the nasal cavity. In botany, it is an indentation or space between the lobes of a leaf.
- An anatomical cavity or hollow passage in an organ or tissue, especially an air-filled space in or around the nose.
- A hollow or cavity within a structure, such as a bone.
- A space or indentation between two lobes or divisions, especially of a leaf.
"The scan showed fluid in one of the maxillary sinuses."
"The doctor said the scan showed fluid in one of the maxillary sinuses."
"The deep sinuses between the lobes give the oak leaf its distinctive outline."
The standard plural is "sinuses."
"The four paranasal sinuses are located in the bones of the face and skull."
The word sinus began with the idea of a fold or hollow, so its anatomical meaning is a natural extension of the shape of a curved passage.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does sinus come from?
The English word comes from Latin sīnus, meaning a bend, fold, curve, or hollow. Its anatomical sense developed from this older spatial meaning, applying the idea of a hollow or recessed space to structures in the body. Related English words include sinuous, sine, and sinusoid, which reflect the same Latin root or its mathematical developments.
Related word forms
How sinus is actually used
The word is primarily technical and is especially common in medicine and anatomy. In general medical usage, "sinus" may refer to a paranasal sinus, while phrases such as "sinus infection" are widely understood. In botany, it is a specialized term for an indentation between lobes.
Easily confused with sinus
A sine is the mathematical function used to describe waves and oscillating quantities, whereas a sinus is a physical cavity, hollow, or curved space.