What does cusp mean?
The word "cusp" refers to a point of transition — the narrow margin between one state and another. Its most familiar use today is in the phrase "on the cusp of," which describes someone or something standing at the very beginning of a significant change: on the cusp of adulthood, of retirement, or of a breakthrough. The word also retains older technical meanings: in geometry, a cusp is the sharp point where two curves meet; in dentistry, it names one of the raised points on a tooth's chewing surface; in astronomy, it marks the horned tips of a crescent moon. Borrowed from Latin, where "cuspis" meant a pointed end or spear-tip, the word carries a sense of sharpness and pivotal moment alike. It is slightly formal in register but widely understood, useful whenever a writer wants to evoke a decisive turning point rather than merely a change.
nounA point of transition between two different states or conditions, especially the moment just before something significant begins. In geometry and dentistry, it also denotes a pointed projecting part, such as the point where two curves meet or the raised points on a tooth's chewing surface.
- A point of transition between two states, times, or conditions; the threshold of something new.
- A pointed projecting part: in geometry, the point at which two branches of a curve meet; in architecture, the pointed intersection of two arcs; in dentistry, one of the elevations on the chewing surface of a tooth.
"She stood on the cusp of adulthood, unsure whether to take the job abroad."
"The country stood on the cusp of a political revolution."
"The molar has four cusps that grind the food."
The plural is regular. It is most common in technical contexts, such as descriptions of teeth or mathematical curves.
"The dentist noted wear on the cusps of her molars."
Astrologers argue over people born 'on the cusp' — but the word originally meant the sharp point where two curves meet, borrowed straight from Latin.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cusp
English adopted "cusp" from Latin "cuspis," meaning a point or spearhead, likely via medieval Latin usage in astronomy and astrology. By the sixteenth and seventeenth centuries it was established in English in technical senses, describing the pointed tips of a crescent moon and the meeting points of curved shapes. Over time its figurative sense — a transitional moment between two states — became dominant in everyday language.
How cusp is actually used
"On the cusp of" is by far the most common modern usage and carries a slightly formal, often anticipatory tone. The astrological sense — being born on the cusp between two zodiac signs — is widespread in popular usage but informal. Technical senses in mathematics, astronomy (the pointed ends of a crescent moon), and dentistry belong to specialist registers.
Easily confused with cusp
"Cusped" is an adjective describing something that has cusps (pointed projections), while "cusp" is the noun for the point itself.
"Cup" is a drinking vessel; "cusp" is a transitional point or pointed tip — they differ only by one letter in spelling.