From Longman Dictionary of Contemporary Englishturn tailturn tailinformalLEAVE YOUR HOME/COUNTRY to run away because you are too frightened to fight or attack → tail
Examples from the Corpus
turn tail• If one animal suddenly turns tail, it is liable to be attacked and might get injured.• He caught sight of a few others, but they turned tail and vanished when they saw him through the mist.• She wanted to turn tail and run, but she couldn't have stood herself if she appeared such a coward. 