What is Arendator?

Legal Definition
Arendator (literally "lease holder") (Ukrainian: "Орендар" (Orendar), Russian: "Откупщик" (Otkupshchik)). The term derives from "Arenda" (Polish: "rent"), a Latin term referring to the lease of fixed assets, such as land, mills, inns, breweries, distilleries, or of special rights, such as the right to collect customs duties,, etc. Trusted individuals were often given such rights to collect rent or revenue and were allowed to keep a portion of the money in exchange for this service, sometimes as a reward for other services to the state.

Many estates of absentee landlords in the Polish-Lithuanian Commonwealth during the 16–18th centuries were managed by arendators. This extremely lucrative fiscal practice was also common in tax collecting in medieval Spain and France. There were frequently problems with corruption. The practice continued in the Russian Empire until the late 19th century.
-- Wikipedia
Legal Definition
A farmer or renter; in some provinces of Russia, one who farms the public rents or revenues;' a "crown arenda-tor" is one who rents an estate belonging to the crown.
-- Black's Law Dictionary