If you're thinking of the historical meaning:
* Subject: A reeve was responsible for a community, so a subject could be considered the opposite.
* Ruler: While not a direct opposite, a ruler could be considered a higher authority than a reeve.
* Independent: In a sense, someone who is independent is not subject to a reeve's authority.
If you're thinking of the meaning of "reeve" as a verb:
* Unwind: If you "reeve" a rope, the opposite would be to "unwind" it.
* Remove: If you "reeve" something through a hole, the opposite would be to "remove" it.
It's important to understand the specific context of the word "reeve" to determine the most appropriate antonym.