"Keep your pecker up" is an idiomatic expression which means keep your spirits high, be optimistic and don't get discouraged. The phrase is commonly used to provide encouragement and support to someone going through a tough time. There are various synonyms that can be used to convey the same meaning as "keep your pecker up", these include "stay positive", "keep your chin up", "keep your head high", "stay strong", "persevere", "pull through", "keep going" and "hang in there". All of these phrases are great to help lift someone's spirits and provide reassurance during difficult times.