結論 = 変わり目（二つのものが交わる点）= 転じて 先端 の意味にもなる
“be on the cusp of something” の形で～の変わり目にあるとか最先端にいる（ to be at the time when a situation or state is going to change）の意味。
今回も「短い語なのに未知の語彙」シリーズ。前に cohort を調べていた際に遭遇した cusp についての簡単なメモ。
用例①
きっかけとなった Wall Street Journalの記事の再掲。黄金時代の幕開け？
This cohort should be on the cusp of their golden years. Instead, their median incomes including Social Security and retirement-fund receipts haven’t risen in years, after having increased steadily from the 1950s.
用例②
次に Reuters の例。まもなくディールになるであろう、という意味（だと思う）。
Secretary of State Mike Pompeo said on Monday he thought the United States and China were “on the cusp” of a deal to end their trade war.
用例③
続いて New York Times からの例。
In 2017 growth was more than 7 percent, putting Turkey on the cusp of becoming what the World Bank classifies as a “high income.”
用例④
もうひとつ New York Times からの例。
But absorbing Alstom proved to be more difficult than expected, and the acquisition increased G.E.’s stake in the power business on the cusp of the market’s downturn.
用例⑤
まだ少し感覚的に理解できていないので、さらに The Economist からの用例。
Once on the cusp of a renaissance, the nuclear industry now risks being sent back to the dark ages. This is the impression that emerges from much of the commentary in the months since the crisis at the Fukushima Daiichi nuclear power plant in Japan. But is this doom and gloom misplaced?
用例⑥
最後に The Economist からもうひとつ。
But this says much about the amiable nature of a cricket crowd and the camaraderie and instant friendships that can blossom through a shared love of the game. And that spirit is a reflection of what you see on the cricket pitch. But now there are great fears about how long this spirit can endure in professional cricket. It is generally accepted that international and domestic cricket is on the cusp of great upheaval. Money is pouring in like never before and it's not clear how cricket will stand up to this onslaught. Change is not something that cricket takes on lightly. The preface to the MCC's laws of cricket states:
