The thumb is what lets the hand grip, so dream books tie it to control, willpower and approval. Being under someone’s thumb is the old reading when it presses down on you.
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.