Collins COBUILD Advanced Learner's English Dictionary - muck up

If you muck up or muck something up, you do something very badly so that you fail to achieve what you wanted to. (mainly BRIT INFORMAL) I mucked up at the 13th hole and told myself that this was getting stupid... Scientists should figure out how to keep the natural world from mucking up the affairs of people. = mess up PHRASAL VERB: V P, V P n (not pron), also V n P