Transmission Part is a term used to describe the components of a vehicle's transmission system. The three crossword solutions for this term are GEAR (4 letters), Gearcase (8 letters), and Synapse (7 letters). GEAR is a toothed wheel or cylinder that meshes with another toothed part to transmit motion or to change speed or direction. Gearcase is a housing that contains the gears in a transmission system. Synapse is a junction between two nerve cells, across which an impulse passes from one to the other.