BU (http://www.lojban.org/en/publications/reference_grammar/chapter17.html)

A suffix which can be attached to any word, typically a word representing a letter
of the alphabet or else a name, to make a word for a symbol or a different letter
of the alphabet. In particular, attached to single-vowel cmavo to make words for
vowel letters.

.abu .ebu .ibu .obu .ubu .ybu a, e, i, o, u, y.

