“on cloud nine”是英语中极具画面感的习语，核心语义为“极度幸福、欣喜若狂”，形容人因某件好事而处于情绪的顶峰，仿佛置身云端，飘飘然难以自持、极致喜悦。其词源尚无绝对统一的定论，但最被广泛认可的说法与气象学相关——20世纪50年代，美国气象局将云层划分为9个等级，“cloud nine” 第九号云指代最高处的积雨云，海拔极高且形态缥缈，这种云通常高大壮观，能给人带来一种宏伟、超凡的感觉，可能由此引申出了处于一种极度愉悦、仿佛置身于云端仙境，人们用“身处第九号云”比喻“抵达幸福的顶点”；多用于非正式场合，口语与书面语中均可使用，语气轻松且情感浓度高。如：
She’s been on cloud nine since she met her new boyfriend.
自从遇到新男友，她就一直欣喜若狂。
When he asked her to marry him, she was on cloud nine.
当他向她求婚时，她欣喜若狂。
She looks on cloud nine after getting the offer from her dream company.
她得到梦寐以求的公司的录用通知后，看起来欣喜万分。
I was on cloud nine after our first date—everything felt perfect.
第一次约会后我欣喜若狂，一切都感觉那么完美。
When she found out she’d got top marks, she was on cloud nine.
当她得知自己得了最高分的时候，欣喜若狂。
The party was on cloud nine after winning a majority in the election.
该党在选举中获得多数席位后欣喜若狂。
Investors were on cloud nine as the stock market hit a new high.
随着股市创下历史新高，投资者们欣喜若狂。
The diplomats were on cloud nine after the successful peace talks.
和平谈判圆满成功后，外交官们欣喜若狂。
The soldiers were on cloud nine when they received orders to return home.
当士兵们收到返乡命令时，欣喜若狂。
I’m on cloud nine. I can’t stop thinking about him.
我欣喜若狂，脑子里全是他。《电子情书》
She was on cloud nine when she heard the news that she was admitted to her dream university.
得知被梦想大学录取的消息，她极致喜悦。（2022年全国高考）
同义替换（按使用频率排序）：
over the moon（最贴近，语气相近，均为口语化表达，例：
She was over the moon when she got the offer.）、
on top of the world（语气相对强，侧重“极度满足”，例：
Winning the game made him on top of the world.）、
in seventh heaven（语气稍弱，源自宗教语境，侧重“精神层面的极乐”，例：
He was in seventh heaven after his wedding.）、
delighted to the core（语气普通，书面化表达，侧重“内心深处的喜悦”，例：She was delighted to the core at the good news.）。
