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

Pandemic restrictions heavily curtailed his first season, while a wave of antitrust litigation challenged the economic foundation of the NCAA and California moved to the cusp of ushering in the NIL era through state-level legislation. — Daniel Libit, Sportico.com, 23 July 2026

The clutter ebbs and flows like the tide, reflecting the chaos of spaces where artists live, often homes just on the cusp between quaint and unbearably chaotic. — Leslie Felperin, HollywoodReporter, 21 July 2026

Also, if this is what the cusp of 50 looks like, please pass the bottle of potion. — Melissa Ruggieri, USA Today, 7 July 2026

Why Our Brains Sometimes Work Against Us Our brains are primed to look for danger—a threat-detection instinct that still serves us in certain circumstances, but not on the cusp of our own accomplishments. — Karyn Gallant, Forbes.com, 30 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