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

Technology is on the cusp of allowing humans to disrupt or steer natural disasters, like hurricanes, according to a new study, which appeared in the journal PLOS Water on June 24. — Doyle Rice, USA Today, 27 June 2026

The series arrives on the cusp of the 250th anniversary of America’s founding, and offers an alternative history that’s still steeped in facts. — Maira Garcia, Los Angeles Times, 26 June 2026

On the cusp of the 250th anniversary of its founding, the United States of America is at a crossroads. — Aramide Tinubu, Variety, 24 June 2026

Up next is Legacy Motor Club’s Erik Jones, whose strong midseason surge has him on the cusp of a Chase spot with nine races remaining in NASCAR’s regular season. — Jeff Gluck, New York Times, 24 June 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