"Seeu" is an informal slang term that is commonly used on social media and messaging platforms. It is essentially a shortened or abbreviated version of the phrase "see you", which is used to express that someone will be seeing someone else again in the future. Some common synonyms for "seeu" include "catch ya later", "later", "goodbye", "adieu", "cheerio", "so long", and "farewell". Each of these synonyms conveys the same general meaning and sentiment, indicating that the speaker expects to see the other person again at some point in the future, but in a more formal or traditional way than "seeu".