by air›TRANSPORTtravelling by or using planes: arrive/travel by air25% of the state's economy is fueled by tourists who travel by air.deliver/send/ship sth by airThe company adds a surcharge for express packages delivered by air.
up in the air›if a matter is up in the air, it is uncertain and no final decision has been made about it: The future of the company has been up in the air since one of its key shareholders was compelled to sell its stake.