A theremin is played without being touched, so it is read as influence at a distance and eerie, otherworldly feeling. Dream tradition links it to the uncanny and to forces you sense but cannot hold.
Does the traditional reading fit your dream, or did it mean something else to you?
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.