The phrase "world of difference" implies a significant and noticeable contrast between two things. Some synonyms that can be used instead of this expression are "night and day," "chalk and cheese," "poles apart," "apples and oranges," "black and white," "heaven and earth," "two worlds apart," "utterly different," "miles apart," and "complete opposite." These synonyms can help add variety to your writing and make your language more descriptive and engaging. They also help convey a clear message about the disparity between two things and the stark contrast in their characteristics.