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The exact point where one thing is about to turn into another — right at the edge of a big change. It's almost always used in the phrase "on the cusp of", meaning "just about to": "on the cusp of adulthood" means almost grown up. Doctors also use "cusp" for the pointed part of a tooth, and use it for the line between two zodiac signs.
邊緣、臨界點（on the cusp of＝正處於……的邊緣）
組成From Latin "cuspis", meaning a point or a spear tip.
原始詞典資料9 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
cuspnoun/kʌsp/
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A sharp point or pointed end.
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An important moment when a decision is made that will determine future events.
- Newcastle were 11 points adrift of Spurs following their 5-0 mauling at the hands of the north London club in February. But a sixth successive Premier League win puts them on the cusp of European football next season as they surged 15 points clear of seventh-placed Everton, who have five games left to play.
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geometrymathematicssciencesA point of a curve where the curve is continuous but has no derivative, but such that it has a derivative at every nearby point.
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architectureA point made by the intersection of two curved lines or curved structures, a common motif in Gothic architecture.
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astrologyhuman-sciencesmysticismA boundary between zodiacal signs and houses.
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dentistrymedicinesciencesAny of the pointed parts of a canine tooth or molar.
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anatomymedicinesciencesA flap of a valve of a heart or blood vessel.
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A point of transition.
- I see freight returning in a big way. The 2016 reconnection of the Helwith Bridge quarries can produce up to three heavy trains a day. The nearby and much bigger Horton quarry is also on the cusp of rail reconnection.
cuspverb/kʌsp/
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slangTo behave in a reckless or dangerous manner.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。