Unbridled – Uncontrolled
Under the horses bridle (unbridled) was a big horsefly that stung it and made the horse uncontrollable.
Examples of unbridled in a sentence
Her unbridled fury frightened them.
Running about with unbridled energy, the child could not be calmed down for her nap.
It became an unforgettable encounter when our raft capsized, and I was swept along powerless in its icy unbridled current.