You could simply say "significant difference." In my experience, "statistically" is typically implied prior to "significant." Also, you should never use the term "significant" except to mean statistically significant. If you want to say the difference is large, you would use another word, like "meaningful" or "substantial."
However, I would say that you don't even need to add a qualifier to the word "different" if the difference is statistically significant. You could just state the difference and report the results of the statistical test. If you are writing an academic paper and claim that two quantities are different, then the difference ought to be statistically significant. On the other hand, if you need to report a comparison for which a statistical test was negative, you would want to make sure to specify that the difference was not significant.