Directly related to "prefer":
* Preferable: More desirable or suitable
* Preference: A greater liking for one thing over another
* Preferentially: Giving preference to something or someone
* Preferential: Relating to or showing preference
Less directly related, but still using the "prefer" root:
* Prefect: A high-ranking official (though the root here is actually "perfect" which is related to "prefer" etymologically)
* Prefatory: Introductory, as in a prefatory remark
Note: The root "prefer" comes from the Latin "praeferre", which means "to carry before" or "to hold in front." This original meaning hints at the idea of something being chosen over others.