What does annuli mean?
Annuli is the plural of annulus, a Latin-derived term meaning rings. The word appears most often in scientific contexts. In biology and geology, annuli are the ring-shaped bands that form as an organism grows — most famously the annual growth rings of trees, but also the rings found in fish scales, ear bones (otoliths), corals, and shells, which researchers count to determine age or growth rate. In geometry, an annulus is the region lying between two concentric circles, so annuli can describe any set of such ring-shaped areas, such as the bands of a dartboard or target. Because the term is precise and technical, it carries a formal, scholarly tone and rarely appears in casual conversation. Its value lies in accuracy: where 'rings' might be vague or ambiguous, annuli signals careful scientific description. Anyone reading ecology papers, anatomy texts, or mathematical writing will encounter this useful plural form.
nounThe plural of annulus: ring-shaped structures or regions, especially in biology (such as growth rings) and geometry (the region between two concentric circles).
- Ring-shaped structures or markings in biological specimens, such as annual growth rings in scales, bones, or trees.
- In geometry, the regions between two concentric circles; plural of annulus.
"Under the microscope, the fish's otolith revealed clearly defined annuli marking each year of growth."
"The geologist dated the coral by counting the annuli deposited each year."
"The target was printed as a series of alternating black and white annuli."
Annuli is itself a plural form (of annulus) and does not take a further regular plural; it takes plural verb agreement.
"The annuli were clearly visible under magnification."
Every tree keeps a diary written in annuli — count the rings and you can read exactly how old it is.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of annuli
Annuli comes from Latin, being the plural of annulus, which meant 'ring' or 'little ring' and itself derives from anus, the Latin word for a ring or circle. English borrowed annulus in the early modern period, initially in heraldic and descriptive use before it became established in mathematics and the natural sciences. It shares this root with related English terms such as annular ('ring-shaped') and annulate ('marked with rings').
Related word forms
How annuli is actually used
Strictly a technical and scientific term, appearing mainly in biology, geology, dendrochronology, and mathematics. It is simply the plural of annulus, so it never stands alone as a singular form. In speech it is far less common than the singular.
Easily confused with annuli
Annuals are plants that live for a single year, while annuli are ring-shaped structures such as growth rings.
Annals are historical records arranged year by year, whereas annuli are physical ring-shaped structures.