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

Leading the Padres 8-5 entering the ninth at Coors Field on Thursday afternoon, the Rockies were on the cusp of clinching the three-game series. —Patrick Saunders, Denver Post, 24 Apr. 2026

This isn’t the terrifying Frost of modernist criticism—although the poem is fully aware of darkness, and its world, on the cusp of World War I, like ours, certainly had its terrors. —Literary Hub, 24 Apr. 2026

Now, hearing the president warn that Iran was on the cusp of a nuclear weapon, Benderman can't help but be skeptical. —Juliana Kim, NPR, 24 Apr. 2026

John Logan’s unfussy screenplay hones in on Michael’s ascent from star child phenom in the Jackson 5 up to being on the cusp of becoming the King of Pop. —Randy Myers, Mercury News, 23 Apr. 2026

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