bu (rafsi bu'i or bus)
- used (either as a suffix or following another word) to form vowel, ".", ",", and non-Lojban letterals
- The word to which this cmavo gets suffixed to becomes a compound cmavo of selma'o BY.
- (Lojban letterals) .abu, .ebu, .ibu, .obu, .ubu, .ybu, denpa bu, slaka bu
- (Miscellaneous) .uibu, joibu, pi'ibu, tobu, toibu, zo'obu
