Definitions:

1. A large rotating wheel with flat boards or paddles attached around its edge, used to propel a boat through water by pushing against it. NOUN
   • The old riverboat had a massive red paddlewheel at its stern.
2. A large wheel fiteed with thick slats, turned by an engine and used to propel a boat. NOUN
   • Tourists gathered to watch the paddlewheel churn the muddy river.

Synonyms:

• paddle wheel
• propulsion wheel
• sidewheel
• sternwheel