Fifth wheel Meaning, Definition & Usage
- 
       noun someone or something that is unwanted and unneeded
       
       
deadwood.
 - 
       noun an extra car wheel and tire for a four-wheel vehicle
       
       
spare.
 - 
       noun a steering bearing that enables the front axle of a horse-drawn wagon to rotate
        
      
 
WordNet
Definitions
- a horizontal wheel or segment above the fore axle of a carriage and beneath the body, forming an extended support to prevent careening.