Brush up on is a phrase that means to improve or refresh one's knowledge or skills. The crossword solutions for this term are 'relearn' (7 letters), 'reread' (6 letters), and 'PAINT' (5 letters). Relearn suggests that one should go back and relearn something they already know, reread implies that one should go back and read something again, and PAINT implies that one should practice or refine a skill.