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

That changed last December, when diplomatic recognition from Israel brought Somaliland to the cusp of a new chapter in its history – one its young writers hope to help shape with their words. — Mahbub Abdillahi, Christian Science Monitor, 3 Sep. 2026

In the north and the south of the county, on the beach and at the cusp of the Everglades, in neighborhoods of all kinds, the number of students attending traditional public schools is down. — Austin Horn, Miami Herald, 29 Aug. 2026

Despite the drop, the 30-year yield is still trading on the cusp of its highest levels in 19 years. — John Towfighi, CNN Money, 19 Aug. 2026

With that, and with their walk-off in San Diego, the Padres leapt from the cusp of the wild-card picture to the thick of it. — Dennis Lin, New York Times, 13 Aug. 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