on a wing and a prayer

Definition

› If you do something on a wing and a prayer, you do it hoping that you will succeed, although you are not prepared enough for it: With scarcely any funding and a staff of six, they were operating on a wing and a prayer.Hoping and hopefulnessPotential

(Definition of on a wing and a prayer from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)