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

• 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

So here’s an album just on the cusp of the new decade into the early Seventies. —Andy Greene, Rolling Stone, 28 Oct. 2025

On Tuesday, Sammon and Britton projected a three- or four-year deal for Alonso valued right around the cusp of the nine-figure mark, which the five-time All-Star might well view as a disappointment the second time around. —Jackson Roberts, MSNBC Newsweek, 22 Oct. 2025

And Laci Kaye Booth and Mae Estes, but I have a feeling all of those girls are right on the cusp. —Jessica Nicholson, Billboard, 16 Oct. 2025

Oh, 6-0 Georgia Tech’s right on the cusp of the bracket (after beating 2-5 Virginia Tech 35-20)? —Alex Kirshner, New York Times, 12 Oct. 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