{f} (Slang) lose faith in oneself or courage to do something (as in "Tom was going to ask Diane out for a date, but he chickened out the last minute"); withdraw because of lack of courage or tiredness
If someone chickens out of something they were intending to do, they decide not to do it because they are afraid. His mother complains that he makes excuses to chicken out of family occasions such as weddings I had never ridden on a motor-cycle before. But it was too late to chicken out