There are 117 5-letter words starting with U in the ENABLE dictionary — 1% of all 8,636 words at this length. U is a one-point tile and the bag holds a lot of them, so these words are less about scoring than about shape: they are what clears a vowel-heavy rack, and in a daily guessing game they are how you test a vowel you have not placed yet.
The list divides into 11 groups by second letter, the largest being the 54 words with un. Scanning the right group is faster than reading the whole list, which is why it is broken up below rather than run alphabetically.
If you know more than one letter, this page stops being the fast way to find it. Enter what you have in the unscrambler — the Contains, Starts with and Ends with filters combine, and setting both length fields to 5 narrows this list to the handful your letters actually allow.