What it means: the law-enforcement officer of a county or other civil subdivision of a state; (formerly) an important civil officer in an English shire
The term is a contraction of shire reeve, which referred to the overseer of workers and tenants in an English shire (equivalent to a county); a kind of steward representing the crown. The shire reeve pretty much had ultimate authority and often was extremely powerful. The same, of course, was true of early sheriffs in the American Old West. In the UK today, the position is either honorary (and unpaid) or has morphed into the High Court enforcement officer, while in the States the sheriff remains the highest law office in a county, with varied authority divisions between this office and those of other law enforcement agencies.
Why I chose it: My combined interests in medieval history and in Westerns, along with love of interesting etymology, make this a natural addition to the (recently much neglected) category of words for thought.