From the Greek "kyklos" meaning circle or wheel:
* cycle: a complete round or series of events
* bicycle: a vehicle with two wheels
* motorcycle: a vehicle with one or two wheels and an engine
* tricycle: a vehicle with three wheels
* unicycle: a vehicle with one wheel
* cyclometer: a device for measuring distance traveled
* cyclotron: a device for accelerating charged particles in a spiral path
* cycloid: a curve traced by a point on a circle as it rolls along a straight line
* cyclone: a system of winds rotating around a center of low atmospheric pressure
* cyclic: occurring in cycles
* cyclical: relating to or characterized by cycles
* cyclopean: of enormous size or strength
* encyclical: a letter or message addressed to the whole church
* encyclopedia: a book containing information on many subjects
* cyclooxygenase: an enzyme that catalyzes the production of prostaglandins
Other words:
* cyclops: a mythical giant with a single eye in the center of his forehead
* cyclorama: a large circular painting or series of paintings creating an illusion of a panoramic scene
This is not an exhaustive list, but it gives you an idea of the range of words that can be formed using the root "cycl."