Ushenna is the sixth letter of the Mandaic alphabet and writes the vowel u as well as the consonant w. It joins on both sides.
With halqa and aksa it makes up the set of three full vowel letters that makes Mandaic a true alphabet rather than an abjad. A separate vocalization mark can be added to distinguish vowel quality, and teaching materials use it far more than ordinary writing does.
Its name is one of the handful in the alphabet that does not follow the pattern of the sound with a preceding a, and the irregular names are a group worth noticing: ushenna, aksa, it, in, dushenna and kad.
Ushenna holds the sixth place, where waw stands in the inherited Aramaic sequence. The neighbouring alphabets use their sixth letter as a partial vowel sign, one of the letters described as mothers of reading, which can stand for a long u or o beside its consonantal value. Mandaic went further with the same letter and made it a vowel outright. The difference between a letter that may indicate a vowel and a letter that is one sounds small and changes what the script is: an abjad leaves the vowels to the reader, and Mandaic does not.
Because ushenna writes both a vowel and a consonant, a word containing it does not tell a reader on sight which is meant, and that is one of the few residual ambiguities left in a script that otherwise removes them. The vocalization mark exists to settle it and is commonly absent, so the reader supplies the answer from knowing the word.