1. Of or relating to vehicles with two wheels
   - two-wheeled

See also: wheel

• Proto-Norse
• proto-oncogene
• protoactinium
• protoanthropology
• protoarchaeology
• protoarcheology
• protoavis
• protoceratops
• protocol
• protoctist
• protoctist family
• protoctist genus
• protoctist order
• Protoctista
• protogeometric
• protoheme
• protohemin
• protohippus
• protohistory
• protology
• protomammal
• protomartyr
• proton
• proton accelerator
• proton magnetic resonance