Illustrated Glossary of Organic Chemistry

Monohydrate: A substance containing one water molecule of hydration. The water of hydration is written after the main formula, separated with a dot.

CaSO4
CaSO4.H2O
CaSO4.2H2O
Anhydrous calcium sulfate
Lacks water of hydration
  
Calcium sulfate monohydrate
Contains one water of hydration
  
Calcium sulfate dihydrate
Contains two waters of hydration