A thorn is read as a small but persistent pain, an irritation or a defence. Dream books often pair it with the rose: beauty and hurt that grow from the same stem.
Has this come up in your dreams before? What was going on in your life then?
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.