precipitous 切り立った、急激に

precipitous は、切り立った、急斜面の、という意味です。具体的には何かが急激に落ちる時の枕詞になっています。7:11 as Graham took me to other alum work on precipitous cliffs, I could see that what at first sight seemed natural was a landscape that have been completely reshaped by this industry. グラハムさんは私を別の断崖絶壁にある明礬（みょうばん）の採掘現場へ案内してくれた。そこは一見すると崖だが、よく見ると明礬製造によって変貌を遂げたことがよくわかる。

U.K. Landscape Mysteries Vol 1 Pt 2

https://www.youtube.com/watch?v=xmJJagNUDCk  3;20 that number dropped precipitously
How and why we need to get the lead out of our lives

https://www.youtube.com/watch?v=3oTjwpsHuuw  4;57 fall quite precipitously
Business of Being a High-End Call Girl

https://www.youtube.com/watch?v=dBXQYMUAIxo  1:02 have dropped precipitously
Pastor Rick Warren on separation of church and state

https://www.youtube.com/watch?v=bvf2FUHCTKM  2:33 the temperatures are falling in this city precipitously.
Superstorm Hurricane Sandy 2012: A Tale of Two NYC's - Going Inside Powerless Lower Manhattan

https://www.youtube.com/watch?v=t78OPbq6pCw  0:48 has dropped precipitously in recent years.
How Should U.S. Postal Service's Financial Problems Be Fixed?

参考リンク
http://bridge-english.blogspot.jp/2011/11/blog-post_05.html  崖っぷちを英語でなんと言うか？