"Andikeni vizuri!"

Translation: Write well!

[Joanne394981]

Why "vizuri" what makes it take the vi- prefix?

[Ernst557459]

*vizuri' is an adverb and hence not declined. As for your question why: I have no idea. You will have to consult a Swahili etymologist to get an answer to that one. It is just another word that you will have to learn.