An imp is read as a small temptation or a mischievous impulse rather than real evil. Dream books link it to the inner voice that suggests a little trouble just to see what happens.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.