?leaving on a jet plane是指乘坐噴氣式飛機離開。它起源于美國民謠歌曲《Leaving On A Jet Plane》，由約翰丹佛（John Denver）演唱，于1969年發行，成為了他的作之一。

用法：

leaving on a jet plane可以作為一個動詞短語使用，意為“乘坐噴氣式飛機離開”。它也可以用來表示某人即將離開某地或者某種情況。

例句1-5句且中英對照：

1. I'm leaving on a jet plane tomorrow morning. 明早我就要乘坐噴氣式飛機離開了。

2. She's leaving on a jet plane tonight to attend her sister's wedding. 她今晚要乘坐噴氣式飛機去參加她妹妹的婚禮。

3. Are you excited about leaving on a jet plane for your vacation? 你對乘坐噴氣式飛機去度假感到興奮嗎？

4. He's been dreaming of leaving on a jet plane and traveling the world since he was a child. 自從他還是個孩子起，他就一直夢想著乘坐噴氣式飛機周游世界。

5. They're leaving on a jet plane to start their new life in another country. 他們要乘坐噴氣式飛機去另一個開始新的生活。

同義詞及用法：

1. take a flight：意為“乘坐飛機”，可以用來替換leaving on a jet plane中的“乘坐噴氣式飛機”這一部分。：I'll be taking a flight to Paris next week.

2. depart by plane：意為“乘飛機離開”，也可以用來表達leaving on a jet plane的意思。：They'll be departing by plane tomorrow morning.

3. fly away：意為“飛走”，可以用來表示某人即將離開某地或者某種情況，與leaving on a jet plane的含義相似。：She's flying away to start her new life in Europe.

4. board a jet：意為“登上噴氣式飛機”，也可以作為leaving on a jet plane的同義詞使用。：We'll be boarding a jet to Tokyo in an hour.

5. take off on a jet plane：意為“乘坐噴氣式飛機起飛”，也可以表達leaving on a jet plane的含義。：They're taking off on a jet plane at midnight.

《飛機起飛》總結：

“乘坐噴氣式飛機離去”，這一詞組，乃是指人即將離開某地或某種境況。其用法與諸如“搭乘航班”、“乘機離開”等動詞短語相通。此語源自一首美國民謠，至今仍為人廣泛應用。本文作者jack，特撰改寫，以模擬魯迅的筆風。