A significant change can refer to a variety of different things. The crossword solutions for this term are 'REDO' (4 letters) and 'MILESTONE' (9 letters). 'REDO' implies that something needs to be done again, usually because it was not done correctly the first time. This could refer to a process or task that needs to be repeated in order to achieve a desired result. 'MILESTONE' is a term used to describe a major event or accomplishment that marks a turning point in a project or journey. It is often used to signify a significant change in the progress of a project or goal.