reservoir (n.)youdaoicibaDictYouDict[reservoir 词源字典]
1680s, "a place where something tends to collect," originally figurative, from French réservoir "storehouse," from Old French reserver "to reserve" (see reserve (n.)). Specific meaning "artificial basin to collect and store a large body of water" is from 1705.[reservoir etymology, reservoir origin, 英语词源]