cusp

noun

ˈkəsp 

: point, apex: such as

a

: a point of transition (as from one historical period to the next) : turning point

also : edge, verge

on the cusp of stardom

… you're on the cusp between heat exhaustion and life-threatening heatstroke.

—Mark Jannot

b

: either horn of a crescent moon

c

: a fixed point on a mathematical curve at which a point tracing the curve would exactly reverse its direction of motion

d

: an ornamental pointed projection formed by or arising from the intersection of two arcs or foils (see foil entry 2 sense 4)

e(1)

: a point on the grinding surface of a tooth

(2)

: a fold or flap of a cardiac valve

cuspate

ˈkə-ˌspāt 

-spət

adjective

cusped

ˈkəspt 

adjective

Illustration of cusp

• 1 cusp d

Synonyms of cusp

• verge
• brink

Examples of cusp in a Sentence

the cusp of a tooth

medical researchers who are on the cusp of a major breakthrough

Recent Examples on the Web

The five conference champions ranked highest are guaranteed a spot in the CFP, and the Broncos ended up being right on the cusp. —Shaun Goodwin, Idaho Statesman, 7 Dec. 2025

But who knew the Aztecs, picked for eighth place in a preseason Mountain West media poll and SDFC, a first-year expansion team, would play their way to the cusp of their respective championships? —Kirk Kenney, San Diego Union-Tribune, 26 Nov. 2025

Looking to the future, Chakkarwar said the pharmaceutical industry is at the cusp of several GLP-1 related discoveries. —Angelica Ang, Fortune, 21 Nov. 2025

Seeing those photos and knowing her acting career was right on the cusp is bittersweet. —Ashlyn Robinette, PEOPLE, 20 Nov. 2025

Word History

Etymology

Latin cuspis point

First Known Use

1585, in the meaning defined above

Phrases Containing cusp

• on the cusp

Kids Definition

cusp

noun

ˈkəsp 

: a point or pointed end or part: as

a

: either of the pointed ends of a crescent moon

b

: a point on the grinding surface of a tooth

c

: a fold or flap of a heart valve

Medical Definition

cusp

noun

ˈkəsp 

1

: a point on the grinding surface of a tooth

2

: a fold or flap of a cardiac valve

cuspal

ˈkəs-pəl 

adjective