Translation: This one pretty much explains itself. If you were to listen to the word she repeats over and over it would appear that she is always saying "Little, Little, Little" which is appropriate for how small she is.

The name itself, when put together as Chibichibi, can mean "making something last; long-lasting or enduring" aka, something eternal, which would be a very fitting name for her. She is the light of hope in the anime, an everlasting light. In the manga she a future self of Sailor Moon, the eternal soldier. Either way it fits very well for her.