I was reading a story in Latin, and part of it said "i nunc, Mercuri". I don't know what i is in Latin. By the way, this line is said in dialogue. Is it a filler word similar to the "umm" or does it mean something else? I am really confused. Thank you for all the help! I also tried looking it up, but I didn't find any good results. What does it mean? Thanks in advance.
Ī is the imperative singular of eō, īre, "to go". So ī on its own means "go!" (as a command to a single person). In this case, the character is saying "go now, Mercurius".
The other one-letter words in Latin (that I know of) are ā ("away from"), ē ("out of"), and ō (used to address someone). As far as I know, *ū is not a word.