Sawdust is the trace left by work, and is read as effort, craft and the leftovers of a finished task. It can also stand for things ground down until little substance remains.
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.