Bicycle made for two (6)
I believe the answer is:
tandem
'bicycle made for two' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tandem that I've seen before include "Two-person bicycle" , "Bicycle-built-for-two" , "Two-seat bicycle" , "Bike for two cyclists" , "Bicycle made for two" .)