We found 18 dictionaries that define the word water heater:

General (13 matching dictionaries)

1. water heater: Merriam-Webster
2. water heater: Oxford Learner's Dictionaries
3. water heater: Collins English Dictionary
4. water heater: Vocabulary.com
5. water-heater: Wordnik
6. water heater: Wiktionary
7. water heater: Infoplease Dictionary
8. water heater: Dictionary.com
9. Water-heater, Water heater: Wikipedia, the Free Encyclopedia
10. water heater: Rhymezone
11. water heater: FreeDictionary.org
12. water heater: Mnemonic Dictionary
13. water heater: TheFreeDictionary.com

Business (2 matching dictionaries)

14. Construction Term Glossary (No longer online)
15. Water heater: Energy Dictionary

Computing (1 matching dictionary)

16. water heater: Encyclopedia

Tech (2 matching dictionaries)

17. Energy Terms (No longer online)
18. Glossary of Common Hearth and Heating Terms (No longer online)

(Note: See water_heaters as well.)

Definitions from Wiktionary (water heater) ▸ noun:  An appliance for heating water above its ambient temperature, generally for domestic use. Similar: hot-water heater, water boiler, immersion heater, feed heater, boiler, calorifier, domestic hot water, hotwater bottle, hot water bottle, superheater, more... Opposite: water cooler, water chiller, water dispenser Phrases: hot water heater, Storage water heater, more... ▸ Words similar to water heater ▸ Usage examples for water heater ▸ Idioms related to water heater ▸ Wikipedia articles (New!) ▸ Words that often appear near water heater ▸ Rhymes of water heater ▸ Invented words related to water heater