A grater wears things down bit by bit, and dream books read it as friction or irritation that keeps scraping. It can also stand for breaking a big task into small pieces.
Where in your waking life have you met something like this lately?
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.