「fleeting」是「瞬間、短暫的」，例如：

As he pushed himself upright he saw a fleeting image just on the other side of the fence.（當他坐直時，在柵欄的另一側看到了轉瞬即逝的景像。）

We only had a fleeting glimpse of the sun all day.（這一整天，太陽只短暫露臉。）

Some moments are too fleeting for clumsy fiddling.（某些時刻太短暫珍貴，不應該胡混過去。）