The nightingale sings in the dark, so poets and dream books read it as longing, love and beauty found in sorrow. It stands for a voice that comes alive when everything else is quiet.
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.