What is another word for "delta"?

Another word for delta depends on which meaning of delta you intend to replace, because delta has multiple distinct definitions. If you are using delta in the mathematical and scientific sense meaning change or difference, synonyms include change, difference, variation, variance, discrepancy, gap, deviation, shift, increment, and differential. For example, instead of saying what is the delta between budget and actual, you could say what is the difference or what is the variance. If you are using delta in the geographical sense meaning the mouth of a river where it fans out into a sea, synonyms include river mouth, estuary, alluvial plain, floodplain, fan, and distributary system, though estuary is slightly different scientifically. If you are using delta as the NATO phonetic for the letter D, there is no synonym, but you could just say D. If you are using delta in finance to mean sensitivity, synonyms include hedge ratio, sensitivity, and exposure. If you are using delta as a verb meaning to leave, synonyms include depart, leave, exit, bounce, and dip. So the best general synonyms are change and difference for the abstract meaning, and river mouth and estuary for the landform meaning. Choose the synonym that fits your sentence to avoid confusion.