air意思是"空氣、天空」，up意思是「在…之上」。與中文詞語「懸而未決、舉起不定」有著一樣的意思，懸在半空沒有著落的事情，說明還沒有定論，尚未成定局，有待商榷。
看看老外聊天時怎麼用up in the air:
A Where are you going for the vacation？
B My plans are still up in the air.I was thinking about visiting my brother in Alaska，but my wife started nagging me about Hawaii.
A 你要去哪度假？
B 我還舉棋不定。我本來想去阿拉斯加找我弟弟，可是我妻子最近開始吵著要去夏威夷。
up in the air例句精選：
He told reporters today that the president's trip to Moscow is up in the air.
今天他告訴記者們總統是否前往莫斯科尚未確定。
How about your interview result? It's up in the air.
你的面試結果怎麼樣？懸而未決。
I am busy, so it's up in the air.
我很忙，所以我還不能確定。
The question of a new trial is still up in the air.
但關於新一次的審判的問題仍然懸而未決。
對某事沒有十足的把握。
leave it hanging 猶豫
I don't want to leave the decision to buy the car hanging forever.I'm tired of riding on the bus.
買車的決定我不想再猶豫下去了。我已經搭公交搭到厭煩了。
on the fence 猶豫
She's still on the fence about settling down，which makes her boyfriend very anxious.
她對要不要安定下來還在猶豫，她男友為此很緊張。