noun

1. a place where anything is collected and stored, generally in large quantity; esp., a natural or artificial lake or pond in which water is collected and stored for use
2. a receptacle or part (in an apparatus) for holding a fluid, as oil, ink, etc.
3. a large supply; esp., an extra or reserve supply
4. Biol.
   1. a part, sac, or cavity in some animals or plants in which fluid collects or into which products are secreted
   2. a species of organism that serves as an immune host for a parasite that can cause disease in another species
      in full reservoir host

Etymology: Fr réservoir < réserver: see reserve